Given all these factors the 8600GTS is a better card than the X1950XT.
Especially at high resolutions, the 8600 GTS will be getting single-digit framerates while the X1950 XT will be doing just fine.
Sure, the power requirements of the X1950 XT will be higher. But BOTH the X1950 XT and the 8600 GTS require a 6-pin power cable. Even taking that into consideration, anyone saying the 8600 GTS is a better card than an X1950 XT is pushing a questionable agenda.
The X1950 XT eats the 8600 GTS alive. No questions asked.