8800 ultra vs 4870 x2

So right now I have one 8800 ultra and one of my friends has a 4870 x2 he is willing to sell me for $100 dollars plus the ultra I use a 1920 x 1200 res screen and I use vista 64 and xp 32bit with a Intel i7 920 will I see big enough performance gains to justify the $100 dollars and ULTRA for the card? I have a big enough power supply to power it and all that i just want to know possible performance gains as I haven't found many good benchmarks comparing the 2 cards.

Heres the cloest I can find. Its a 8800GTX, a tad slower than your ultra, compared to 2 4890s in CF, at least 10% faster than the 4870x2. Its ball park numbers, but itll give you a hint of what youre looking at. Id say 2 to 3 times the fps will be seen on average
http://www.firingsquad.com/hardwar [...] /page6.asp

I was in the same situation,i had a 8800GTX(A downclocked 8800ULTRA) and i switched to a HD 4870X2 and i am very happy with the way it performs (i play @ 1680x1050 first but now i play @ 1920x1200 and hopefully i can play every game out there maxed out and smoothly ) so defenitely do it,it will give u a big boost