X1950PRO or 8600GTS ???

X1950pro

while the 8600GTS is DX10 capable, it's performance in DX10 games is pathetic. You would have to upgrade anyway when you want to play DX10 games.

I vote for pro by a fairly big margin

I would say you would have to go with the X1950 Pro. It is faster than the 8600GTS in direct X9 games and it is a WHOLE lot cheaper. The 8600GTS is definately over priced.

Remember: 8000 series Nvidia cards and the HD 2900 ATI cards are verison 1.0 when it comes to Direct X10. There are basically no Direct X 10 games out right now. Also I heard the 8800 GTX video card got poor benchmarks in Crysis. I think once Direct X10 games come out (really good ones that is) that people will have to SLI or Crossfire the current DX10 cards that are out right now to get DX10 games to perform the way they were meant to be played. I think the first really good Direct X10 card will probably be the Nvidia 9800GTX due out this November.

I would get a X1950 pro if you are building now and wait for the next Generation of Direct X10 video cards to come out next year.

You would be short changing yourself to get a 8600GTS right now because:
1. The card is new and the drivers probably are not at perfection
2. It is not going to be able to run direct X10 games at the level you probably would want it to
3. You would be over paying for the card. What you are paying for is new technology that has virtually no practical application at this moment.
4. It would be slower than an ATI 1950Pro at Direct X9 games
5. 8600GTS only has a 128 bit memory interface compared to the X1950Pro's 256bit memory interface.

BTW at the end of August Catalyst is coming out with new drivers that from the betas show a significant increase in performance for all ATI X1k and X2k cards.

Also, I would go with a more reputiable brand like Sapphire or Power Color for a X1950 Pro.

Here is a killer deal

$136.99 for a 256MB Card
http://www.newegg.com/Product/Prod [...] 6814102061

$152.99 for a 512MB Card
http://www.newegg.com/Product/Prod [...] 6814102075

If you are running Vista I would go for the 512MB card.
The card is fully Vista compliant

That is a lot better price than paying $169 for a 256MB 8600GTS

Yeah, I wouldn't bother with the 512mb version. I haven't seen any evidence that the extra memory helps with Vista.