Reflex does some funky things in the name of latency but in essence you are getting the latency benefits of no vsync without the obvious downside of frame tearing. It's gonna ignore your chosen framerate cap and do its own thing but one of the ways it fights latency is by enforcing a gpu utilization limit, since that has it's own latency implications, so it's not like it's gonna burn down your gpu (rhythm games are largely cpu-bound anyways so in most instances it should have no bearing)