Yep - the 8800 would be the suggestion from me. I only opted for a another 7900GTX recently, simply to match the one I already had in the case.
I forfeited DX10 functionality for the chance of SLi. When games truly utilise SLi (rather than merely acknowledge its presence) then the difference is amazing. I retried CoD2 with the 'SLi optimization' option ticked - fecking hell!
My theory is that if you're starting afresh with a new card, buy the best you can afford. That way, when the tech price drops in approx 6 months, you can pick up the same card for roughly half the price - and double the spec (almost!) Worked for me, anyway.
D.