I thought I might note I found XRS to have a large impact on my FPS. However I never reported it as it was only the one case and I haven't had a chance to properly test it (missed a couple of raids).
I believe all Ace addons can be put into standby mode so it's fairly easy to test which one is giving the fps drop. Just put each on in standby until the situation fixes itself, it should be fairly obvious when it does (fps going form sub-10 to 30+ is a AMAZINGLY obvious change).
Not need to log in and out constantly like with non-ace addons :)
Could you check that please? (with /xrs standby)
I don't have any performance issues running it (even with my buff icons currently, which are relying on many UNIT_AURA events handled by SpecialEvents). And as I said before: XRS only updates after a given time (0.1-1.5s), between this time, my bars are flagged as dirty, and I update them after the time runs out. Maybe you have created too many bars?