Spring RTS Engine

I'm quite sure there is no way i could did it wrong. I tried both turning off threading optimisation for "spring.exe" and turning it off in global settings.

already did, no effect

Windows XP with sp2

I'm using same options, except for 3d trees - i had to turn them off beacuse they caused strange bugs.

no, but I've just tried what was written there - no effect

I have nvidia 8800gts and core2duo E6550, which should be more then enough for Spring. But in large games framerate drops dramatically, it even becomes unplayable. And ideas why this happens? I turned shadows off and its still the same. Also, I've installed latest drivers, no effect.