Funny that my 8800gt seems to be beating my 4850(got for free b-day) on all my benchmarks.
lightsmark08 8800gt-441.5fps 4850-301.9 fps
3dmark06 8800gt-10547 4850-10405
3dmark vantage 8800gt-6404 4850-6109
even my games seem to run smoother.
Cleaned out all the old drivers and running the newest ones.
perhaps the 4850 doesnt like my chipset. nforce4.
Vista 32-bit/ x2 5600+ oc to 2.94Ghz/ 2GB G.Skill PC6400/ Evga 8800gt superclocked gpu-700Mhz mem-954Mhz
Gigabyte m55sli-s4/ hitachi deskstar 320GB hd 7200rpm
All the benchmarks you see on the internet that show a single 4850 beating the TriSLI GTX 280 @ 4096x7518 resolution and 152QXSMPAA and 9805UltraAF are AMD biased whores spilling lies into your very soul
It is likely that your CPU is bottlenecking the cards
the 4850 normally runs at 600Mhz so does the 8800gt.(superclocked at 650) i overclocked both to 700Mhz and the memory was the same as well. the cpu was overclocked to 2.94 as well in both configurations. this was also a fresh install of vista. i just have a feeling the 4850 doesnt like my chipset very well.
The 4850 runs at a stock of 625Mhz core and 993Mhz GDDR3.
I have an A64 X2 4400+ @2.4Ghz with a 4850 running smooth. I don't know if a 8800GT would do better, i don't have one to do that, but i can tell you to check in the CCC, under 3D settings what you have on and what not.
If you run with AA or AF in games, and have them on in the CCC, your card will be doing double work.