I have had both of these cards.
I have the EVGA 8800 Ultra stock speeds with a Q6600 at 3.0 and I got around 13,500 or so 3dmark06
I have EVGA 8800GT superclocked in SLI with a 680i LT motherboard running on a Q6600 at 3.0 and I got 15,200 3dmark06.
UT3 and COD 4 run higher FPS and are butter smooth on my 8800GT SLI rig, but in Crysis my 8800 Ultra runs it a lot smoother than the 8800GT SLI rig.
The Ultra throws out a ton of heat, in fact it runs my P180 case pretty hot with four case fans running, where as the 8800GT SLI setup seems to run cooler.
To be honest I love my ULTRA, it is an awesome card, but you can get the same or better performance out of 8800GT SLI. The only problem with 8800GT SLI is there no room for an upgrade. You want my honest opinion. Get one 8800GT for now and save some cash and buy the 9800 series when it comes out.
Hope this helps
Sparkarrestor