The Steam version comes with the first two patches already integrated, so my experience so far has been very smooth. Granted, that's only about 45 minutes of gameplay so far.
I found a good performance balance for my:
Remember, these are settings that look much better than the original. "Regular" dynamic lighting even looks better than the original. Anyway, my settings are set to:
-Enhanced dynamic lighting (*NOT* DX10)
-Turn grass distance down a bit
-Turn shadow quality down a bit
-Didn't change anything else from where they started
-1680x1050 resolution, no AA
Gives me FPS fluctuating between 20-60 depending on the situation, remains playable throughout.