Took out courtiers of vassals as choice for guardians this brings the list of candidates down by a huge number but 1. it's more realistic and 2. it stops the huge FPS drops everyone experienced.

See the Discussion topic about it, this is option 1 that I talk about in the discussion.

Let me know how it works for you.

Updated for 1.6 version of the game, let me know if there are any problems