Have you set the graphics settings to as low as you can, using the
low quality rendering engine? Rift is quite demanding and doesn't
give very high FPS even on quite powerful computers running Windows.
I hear performance improvements are in the pipe for the next release of crossover, but I confirm this from native vs crossover testing on a brand new macbook pro..
While it's possible to use higher settings on windows, the FPS in group combat (in other words, when it matters in an MMO) will still reach the same levels, sometimes lower, than crossover.
In short, it's a very new game, and trion still has some optimization to do.
idiosychrosies i've noticed in the game compared to more mature titles:
group frames cause fps to tank under their newer rendering engine
spell effects have a much higher penalty on performance than they should
I'm hoping trion has at least a few people on optimization.