Certain objects are extremely badly optimized in Xsyon. On my high end machine the game normally runs @ 150-200 FPS. However, when I look at some objects, my FPS drops to exactly 30 FPS.
Lame.
The first day of rift beta the FPS was like 20 on max. It'll take a little more time to optimize xsyon. However, I don't run completely maxed as you don't see drastic differences with all of the settings. I cannot see any screen lag.