keep in mind that my GTS is basically a GT with all shader processors enabled (i think 112 (GT) vs 128 (GTS)), the 640mb and 320mb GTS's used the older G80 core while the GT and 512mb GTS use the g92 core, it was a stupid naming scheme on nvidia's part that caused a bit of confusion
320GTS < 640GTS < 512GT < 512GTS < GTX
the cooler+card takes up ~2 slots as far as height is concerned, like most of the higher end cards
as far as depth is concerned, it really won't interfere with anything, i have an Antec 900 case with a side fan installed, there's plenty of gap between the cooler and the fan