I did this a while ago (beginning of March). I'm sorry I didn't benchmark real games.
I don't have the cards anymore, but I wrote down the scores (screenshots).
My system is the same, same OS installation, etc. Only difference was the cards:
7800 GT SLI 3D Mark 2005 11701
7800 GT SLI 3D Mark 2006 6408
X1900XT 3D Mark 2005 10783
X1900XT 3D Mark 2006 5289
7900 GTX 3D Mark 2005 10585
7900 GTX (715 / 1790) 3D Mark 2005 11176
7900 GTX (715 / 1790) 3D Mark 2006 6466
7900 GTX (715 / 1790) SLI 3D Mark 2005 13572
7900 GTX (715 / 1790) SLI 3D Mark 2006 8893
7900 GTX 1920x1200 4AA 8AF 3D Mark 2005 5923
7900 GTX SLI 1920x1200 4AA 8AF 3D Mark 2005 10643
7900 GTX SLI 1920x1200 8AA 16AF STRAA 3D Mark 2005 4478
I'm not telling here that one card is better than the other. Just want you to have the numbers I got. This took some time also.
Meanwhile, I kept only the GTX, no SLI. But I was difficult to choose GTX x XT.
I don't have the cards anymore, but I wrote down the scores (screenshots).
My system is the same, same OS installation, etc. Only difference was the cards:
7800 GT SLI 3D Mark 2005 11701
7800 GT SLI 3D Mark 2006 6408
X1900XT 3D Mark 2005 10783
X1900XT 3D Mark 2006 5289
7900 GTX 3D Mark 2005 10585
7900 GTX (715 / 1790) 3D Mark 2005 11176
7900 GTX (715 / 1790) 3D Mark 2006 6466
7900 GTX (715 / 1790) SLI 3D Mark 2005 13572
7900 GTX (715 / 1790) SLI 3D Mark 2006 8893
7900 GTX 1920x1200 4AA 8AF 3D Mark 2005 5923
7900 GTX SLI 1920x1200 4AA 8AF 3D Mark 2005 10643
7900 GTX SLI 1920x1200 8AA 16AF STRAA 3D Mark 2005 4478
I'm not telling here that one card is better than the other. Just want you to have the numbers I got. This took some time also.
Meanwhile, I kept only the GTX, no SLI. But I was difficult to choose GTX x XT.