iMac 27 - 4850 ATI - Optimal Starcraft II Settings

You should run the base texture setting on "High", not Ultra. High is built for a 512MB card, whereas Ultra is for a 1GB card.

Otherwise, everything else can be set on Ultra.

Under windows, going from high to ultra on textures for the 4850 only affects fps by like 2-3. Not only that, but asides having the game at native resolution and having shaders set to medium/high, texture quality is probably the biggest thing you could do to improve the look of a game.

The biggest thing you can do would be setting shaders to high, instead of ultra. It will gain you around 6-8fps, while leaving everything virtually unchanged. (ultra shaders do make some things appear more realistic, but as far as the general game goes, they are more or less a placebo)

I have overclocked my mobility 4850 to deskto 4850 standards, and run native resolution with everything set to ultra (spare shaders to high) and I get fps at 35-40 on average, according to fraps benchmarking. With those same settings on a default clocked mobility 4850, you can get around 25-30fps on average, which is enough to play the game smooth.