An interesting premise. Looking for a cheap PCI-E card to tide you over until you make a bigger upgrade for Vista?
I don't disagree with the logic. I think it's reasonably sound. But the devil is in the details.
It all boils down to WHEN. When are you planning on getting that DX10 card? I suggest to you that one of the big factors in that answer is "when I have a real use for it".
Vista and Direct X10 games represent a very sharp break with the past. DirectX 10 is a major "reset" of the DX pipeline and there are serious questions of how well the market is going to be able to accommodate it. It is even possible that this "clean break" approach with DX10 could outright fail.
The base requirements for DX 10 is such that there is no going back. If you create your game for DX10 - you don't have a fallback support for DX 9.0c or b hardware. This is a big - nay - massive departure.
In fact, that's a DAMN scary propoosition if you are a developer. You are seriously limiting your potential market if you develop a pure DX10 game (leaving aside parallel hybrid development).
There is also the issue of Vista itself. While I do think that the current installed Windows XP base will migrate to Vista - I think it will be 18 months or so before this reaches critical mass.
Put another way - you won't have a good reason to purchase a DX10 card i.e., to play DX 10 games - for about 18 months or so, maybe as much as 24 months.
18-24 months is long time in computer hardware and gaming. If you were thinking "I'll get a DX10 card in 6 months" then that, I think, is going to lead to a different purchasing strategy then "I'll get a replacement card in 18-24 months".
Best PCIE-E option:
Three weeks ago, I would have recommended the 7900GTO for $253 as the best overall card for you to get. It's essentially a 7900GTX with slightly slower memory - in other words - while not quite bleeding edge, it was leading edge at an awesome price. Best card for the money, bar none.
Problem is - everyone recognized that for being true and they pretty much instantly sold out. You can't find the damn things anywhere. The recommendation was so obvious everybody snapped these up as nVidia dumped these cores and they are GONE.
Solution?
The 7900GT is on sale right now, after rebate, for $199. That's a SIGNIFICANTLY better card than a 7600, which in my view, is a card you do not want. It's got the cachet of a 7xxx series model number, but it is a pale imitation of the 7900 model line. The 7600 is a paper tiger. It's the card you want if you think you are getting a DX10 card in 6-9 months. But I don't think so, I really don't. As explained above, I think you won't have a need for a DX 10 card for quite a while.
The 7900GT is a damned snappy card and at $199 - you'll be pleased with the price and performance now - without having sunk too much $$ in that buying a DX10 card 18-24 months from now will seem to be a waste.
Link for the $199 7900GT at Newegg is here:
http://www.newegg.com/Product/Product.asp?Item=N82E16814150195