I don't know but according to the benchmarks in techreport, two 7900GT in SLI performed better than 8800GTS in Quake4 and FEAR. In the other games the 8800GTS performed better
X1950xtx performed equally to 8800GTS in FEAR
7950GX2 performed better than 8800GTS in FEAR and quake4
http://techreport.com/reviews/2006q4/geforce-8800/index.x?pg=14
I can agree that 8800GTX can outperform any previous card in SLI/CF, but the 8800GTS performs equally to 7950GX2 and a little better than X1950xtx
But since 8800GTS supports DX10 and newer technologies, then 8800GTS might perform better in future games than the previous card in SLI/CF, but currently it can not.