Here are some test compareing which I have done over the past couple weeks (mind you the 7800's are with a T2500, and the 7900's are with a T2600)
7800GO(450\600 1.25v) 3Dmark05 = 6205 Oblivion Higest FPS 17 (med)
7800GTX (430\600 1.3v) 3Dmark05 = 7462 Oblivion Higest FPS 26 (max)
7900GS (600\600 1.24v) 3DMARK05 = 8967 Oblivion Highest FPS 23(med)
7900GTX(600\700) 3Dmark05 = 9640 Oblivion Highest FPS 34(Max)
These are my best 05 scores I did and the best quality settings oblivion auto-set with fPS usinf FRAPS I have owned all 4 cards at a time in my DELLS.
Sold my 7800 Go for $249.95 and Bought a Brand new 7800GTX for $270
Sold my 7900GS single Pipe for $269 and bought New 7900GTX for $499
*Well worth the upgrade for price to performace ratio, I think.
My Laptop: E1705
\T2600(2.16MHz)\2GB DDR2-667\7900GTX(600\1400)\100GB Hitachi SATA 7200\WUXGA+\SB Audigy HD\Intel Pro WiFi+Bluetooth\DVD-Burner\PA-13 130watt Power Supply
Wife's Laptop(my old one): 9400
\T2500\2GB DDR2-667\7800GTX (430\1200)\100GB Hitachi SATA 7200\WXGA+\SB Audigy HD\Intel Pro WI+Bluetooth\DVD-Burner PA-10 90 Watt Power Supply<!-- / message -->