I got decent speeds with Xtreme Racing when running 2x1 and about 80% of the screensize with my Blizzard 1230/32mb.
Can't help you with the screencorruption. Maybe a make a screengrab and post it here so we can see what the problem is. All I can think of are corrupt textures caused by a corrupt lha archive. Orrrr worst case, corrupt memory?
Good luck
