I'm pretty sure you got this all wrong.i think in performance wise, the test so far have shown this for the top end cards.
2 x X1900XT (CF)
2 x 7800GTX 512 (SLI)
2 x 7800GTX 256 (SLI) *Debatable
X1900XT
7800GTX 512
2 x 7800GT (SLI)
2 x 1800XT (CF)
x1800XT
7800GTX
7800GT
X1800XL