I've got a 3640 and CV64 too (and a Buster rev. 11), it's ok in 256 colours at 800x600 and a 16 colour backdrop - any more seems to make it lethargic (doesn't crash on any settings). Is this typical? I've been putting it down to the speed of the memory ...
Oh yeah, I've still got CGX3, dating from the days when P96 was slow on CV cards - is the current version of P96 better now? (don't really want to get CGX4)
I've also lost my manual (and box :-(), when I find it I'll scan the lot and convert into PDF, promise ;-)