is it better then the 320mb 8800gts oc?
The early reviews seen on the new lineup pointed at the R600 model chip seeing a performance gain even over the 8800 series cards. The make of the card using the same chip is one thing to go by for this. While looking over the RX2600XT models offered by Sapphire, Asus, and MSI MSI took the lead with seeing a faster core clock and faster memory clock on a GDDR4 model card. Here that was seen just after ordering the GDDR3 version that selling fast.
The 2900 series is the higher end models for ATI. The RX2600XT had a 850mhz core compared to the 8800's 750mhz and saw a 2300mhz memory over the NVidia model's 2100mhz memory clock. Look over the specifications between makes and models at things like these. NVidia is still a performance driven type while ATI has worked more on improving image quality. OCing always veries between different model cards by diffferent makes.
Can't compare specs between cards, architecture is too different to come to any sort of realistic conclusion. To compare different cards one need to focus on benchmarks.
It doesn't take much to know that one model card with a 1400mhz memory clock won't be quite as fast as one seeing a 2300mhz clock will be. Benchmarks have their limitationa as well since each game driven benchmark only shows results for one game or one program on a limited selection of cards tried.
You could have 2 similar NVidia and ATI cards compared and simply see one win out simply by the other seeing a lower core and memory clock by choice of make. Brands like EVGA, MSI, BFG, and a few others usually fare better over others simply by things like that making the difference.
I found this
http://www23.tomshardware.com/graphics_2007.html?modelx=33&model1=857&model2=778&chart=279
this shows the 320mb better and the gtx way better
Benchmarks do not show only one game, they show many, making sure to include many genres of games too. They also show many different comparison cards as well. they are clear and precise indicators of performance.
Comparing cards simply by looking at the specs is much harder than you allude to, Giving the same line of thought the HD 2900xt would be worlds better than the 8800gtx, giving that it has 320 stream processors, a higher core clock, and only a slightly lower memory clock. Obviously not true. Comparing cards by their specifications is a fools errand, you will make many mistakes. The obvious exemption would be when comparing cards of the same core architecture, such as G80's.