I hate how people still say 8600's suck just cause all the reviews were when it cost $200.. Draw your own conclusions, don't just take it from whatever you effing read.
An 8600GTS is the same thing as the 8600GT except clocked lower and when overclocked the GT slightly beats the GTS stock. (the GTS does have more overclocking potential though but it's not worth it since you seem to be on a tight budget). And at those speeds, it compares to or beats the X1950Pro and also gives you DX10 as an added bonus + new video decoding tech.
It is true however that you shouldn't buy these cards if you're looking for them to play DX10 games well but I'm sure they will play them decently enough.. You obviously won't be playing Crysis with max settings with AA/AF but med-high + tiny bit of aa/af at a lower resolution seems to be reasonable. Unoptimized, it's been shown that a GTX can play it max with a high resolution well so I think the 8600's will do ok.. And the DX10 stuff so far that's been released has only been ports or patches so you really can't say from them who demanding dx10 will really be.