7800 GT SLI woes

Right. Well. I have a 7800 GT in my system now, works like a dream with Counter-Strike and the likes. I was thinking of upgrading my system a bit more and holding off until next year to just gather a whole new system with the 9 series and AM3 chipsets, blah blah.

Seeing as how I wanna get one more year out of my system, I'd like to up my video juuuust a bit for when Age of Conan finally comes out, and maybe a few other games. Since I enjoy the 7800 GT so much, I thought "Hey, I have an SLI board, I don't have any DirectX 10 only games, nor do I have Vista. Why not simply grab another and make use of SLI!"

My concern is this. I can't find any 7800 GT cards to purchase, save those on eBay, and those on eBay have different factory overclocks. Could I underclock/overclock one card or the other to make them compatible in SLI, or will that be haywire on the system and produce unstable results? I know they have to be identical in specs (the card I have now is http://www.3dfuzion.com/cards_7800GT_pcie_256.asp )

I don't really have any desire to play with DirectX 10 features like in Bioshock. I know they spiffy and great, but my budget is only about 150 bucks or so, and I don't want to upgrade to an 8600 GT or anything similar. I feel the performance gain of those cards just for DirectX 10 support isn't worth the investment.

Back to my main question. Can I overclock/underclock one of the cards to symmetrical specs to work, or am I stuck with looking for a new card?

Thanks for your time,

Draylorre


I should probably add, I have a 20 inch widescreen monitor with native 1680x1050, hence the need for upgrading my graphics a bit. Playing those games with full settings runs smooth enough, but I fear for games like Supreme Commander and Bioshock (which my friend is buying for me) and Age of Conan, hence the uppage. Didn't know if I made that clear!