Crap... I typed up a reply to thing last night, but it didn't seem to stick.

Long story short... I tried to duplicate your slow down in both Half-Life and Unreal2 with no luck. They are both translucent sprites (the cig smoke is a sprite base particle effect) but I don't see why they would slow down too much. The only chip-set I know that has horrible problems with overlapping translucency is the old PowerVR... the one used in the DreamCast.

Sorry... uh...have you read the FAQ?