Minimise overall RAM usage
Use Windows' task-manager (Ctrl+alt+del > Start Task Manager > Processes) to identify and close down any non-essential background processes that may be consuming RAM. Web browsers in particular are RAM-hungry these days. Ideally the only things that will be running while you play Bannerlord are Steam anything essential to Windows, as well as any software that may help enhance performance.

Launch Steam with -no-browser
Steam contains its own browser. If you've ever looked at Task-manager while running it, you'll have noticed multiple instances of "Steamwebhelper.exe", each eating a non-trivial amount of RAM.

Steam can be launched with its browser disabled - preventing use of the store, library, community etc (Friends list and chat still works) - by launching it with the command line parameter -no-browser - The steam client its self will then be the only process it starts, minimising its RAM usage.

I advise creating a new shortcut to Steam. Right-click this new shortcut, click Properties > Shortcut, and in "Target" append -no-browser, as such:


You can make this shortcut start Bannerlord directly by appending -applaunch 261550, as such:


With this shortcut set up, you will close Steam and launch it via the shortcut when going to play Bannerlord. You could even rename it and/or set its icon to that of the game to avoid confusion.

Note: I can't tell you whether this affects multiplayer - I'd appreciate someone (who knows they can already login without issue) testing it out.

Restart the game frequently
It's pretty clear by now that the campaign suffers from memory leaks. Reloading save-games, playing through multiple battles/scenes seem to increase RAM usage over time. If the game's performance feels significantly worse after an hour or so, restarting once it reaches this point should keep it within the realm of playability.
Patch 1.0.4 introduces a fix for "a" memory leak issue


Install Bannerlord on an SSD
SSDs are read much faster than regular hard-drives. This means it takes less time to access things like textures, models, sounds and other game assets. If you have one and can free the space, installing/moving Bannerlord to an SSD as opposed to a HDD is almost guaranteed to significantly decrease load-times and mitigate or even eliminate stutter. In my case it was the single biggest improvement.

120gb SSDs go for relatively cheap (Around £30-50) these days, and are probably the most bang-for-your-buck if you currently only have an HDD.


Check your page-file
Windows' Pagefile is essentially an extension of RAM by way of your Hard-Drive/SSD. The pagefile can be dynamic in its size - as it's increased or decreased, RAM and CPU are used to perform this operation.

As such, I'd advise setting the minimum and maximum page-file sizes to the same value. As to what that value should be, most sources indicate 1.5x the size of RAM - That makes it a 12gb (12,288mb) pagefile for a system with 8gb RAM.

For Windows 7:
Control Panel > System and Security > System > Advanced System Settings > Advanced > Performance > Advanced > Virtual Memory.
Uncheck "Automatically manage paging file size for all drives"
Click "Custom size", put 12288 in both boxes, click "Set" then "Apply".

If you have an SSD, moving the pagefile over to it (and reducing the one(s) on your hard-drive(s) to ~500mb) may also make a significant difference.


Disable Audio Enhancements - Use regular headphones/speakers
Don't know why this works, but I'm not gonna complain.
Go to Control Panel > Sound > Playback devices
Right click > Properties > Enhancements on your speakers/headphones
Check "Disable all enhancements". Apply.

In my case, swapping from my USB headset with integrated soundcard to a regular pair of headphones reduced stuttering quite a bit.

Thanks to reddit users ZeppKfw and Gaben_money


Optimise game settings
Ultimately, every system's going to be different in some way - There's no fix-all set of settings that will work better for everyone. However, some settings are more RAM-intensive than others. Here's the key settings I use to minimise stuttering while largely preserving graphical fidelity:

Low:
Textures, Shadows, Environment, Terrain, Decals, Water

Medium:
Particle Detail, Particle Quality, Foliage Quality, Character Detail

High:
Shader Quality, Lighting, Texture Streaming Budget (V. High if you have the V-RAM for it)

Shadow Type - Static Only
Antialiasing - SMAA
Texture Filtering - Anisotropic 16x
Occlusion - TSAO
Shadow Filtering - PCF
Sound Channels - 128

Enabled:
Depth of Field
Screen-space Reflection
Sunshafts
Subsurface scattering
Tesselation
Bloom
Film Grain

Edit: Since moving to an SSD, I was able to put up all the settings listed as Low to Medium with no issue.

It's been reported that using Fullscreen instead of Windowed Fullscreen, and also setting your resolution manually (instead of "Desktop Resolution") also has a significant effect on improving performance. It made no noticeable difference for me.

In any case, I recommend playing around with the settings to find what works best for you. You might be able to get away with increasing some settings, and/or you may need to decrease some for optimal performance. Trial and error is the name of the game.

My specs for reference:

Thanks nemesis234 and Askorti


Windows Readyboost
This is probably grasping at a straw, but every little helps right? Windows Readyboost requires the use of a USB/Flash drive, essentially using it as additional RAM. Flash memory is quicker than reading/writing to the HDD, as is the case with the page-file, but is still no replacement for RAM, and likely isn't as efficient as an SSD's page-file.

Plug in your flash drive.
Clear any unnecessary files
On Autoplay, click "Speed up my system using Windows Readyboost"

Edit: I've been trying this out myself, and I'm not sure if it's been a benefit or if it's caused more issues. I can only guesstimate, but it may be that this USB flash memory is being used over the SSD's pagefile, worsening performance. But I have no real evidence to prove or disprove that.
If you don't have an SSD, it may still provide a benefit, if a small one.

Defragment your Hard-Drive
If, like me, you've had the same HDD for multiple years, chances are it's fragmented to hell and back. As my understanding goes, this means it will take longer for your system to read from the drive, as such compromising performance.

I recommend using Defraggler for this process, however Windows has its own tools for doing so.
Note, it can take up to days to fully defragment a HDD.

https://www.ccleaner.com/defraggler


Update your GPU drivers
Newer GPU drivers tend to be optimised for new high-profile releases.

https://www.nvidia.co.uk/Download/index.aspx?lang=en-uk
https://www.amd.com/en/support


Overclock your RAM
See the last paragraph of the disclaimer.
Ultimately, this is unlikely to make a significant difference, and may well reduce the lifespan of your RAM for the effort, but may be worth a try nevertheless. Proceed at your own risk.

https://www.howtogeek.com/439140/how-to-overclock-your-computers-ram/

Memorycleaner
Memorycleaner is an application that can help cut down on unnecessary RAM usage. In my case, it has helped lengthen the time before the memory-leak becomes a significant issue - however it may contribute to an issue I've had with troops being invisible for the first few seconds of a battle.

https://www.koshyjohn.com/software/memclean/
Thanks Nekolacek

Process Lasso
Process Lasso is essentially an extended task-manager, allowing you to set default rules regarding CPU and I/O priority for each application on your PC. I personally set both to "High" for Bannerlord. Note that some features are unavailable in the free version, but they (probably) have little value in this context.

https://bitsum.com/


Intelligent Stanby List Cleaner
"The application will monitor and clear the memory standby list according to the configured options parameter you set."

https://www.wagnardsoft.com/content/intelligent-standby-list-cleaner-v1000-released
Thanks TOC1775


Razer Cortex
According to TechRadar:
Razer Cortex [...] performs the usual housework (deleting temporary files, emptying the Recycle Bin, checking for broken registry entries and so on), it also suspends non-essential processes to free up RAM while you're gaming.

https://www.razer.com/cortex
Thanks uncnzrd


If you've any other such tweaks throw them in here and I'll add them to the original forum thread. Corrections are also welcome, I don't have much more than a layman's understanding of computer hardware/software, and might have parroted something incorrect. In any case, I hope this helps some of you - Either way, please respond with your specs, the parts of this guide you followed (and anything else you may have done), and whether it made a difference.