slow speed x mac osx 10.6.6 x SMG

[neverendingstory]

Hi everyone, I hope you can help me, I run Dolphin R7171 on an
Imac 27" Intel Core i5 2,66 Gh

4 Go Ram

1 To HD

snow leopad 10.6.6

ATI Radeon HD 4850 512 Mo


And games are too slow (SMG exemple):

FPS: 30
SPEED: 50 %

Is it a problem from OpenGl, from my graphic card capacity ? We can't add plugins in Dolphin mac version to fix that ? Did you find a solution for slow games on osX ?

Screenshot in attachment



Thanks for answers