The 2900 Pro usually has more Memory (512). The 256 bit bus is not really a limiting factor if you compare it to the 512 bit pro. In addition there are many modded bios files and forum threads about overclocking it around.
I have seen some benchmarks showing the GTS(320) running out of memory which comes with a nasty FPS drop. I would go for the pro.
It would be a waste of your money to buy a 320MB GTS. You could upgrade to a 512MB GTS though, as it is the best one.
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Exile- Kreia what are you Jedi or Sith?
Kreia- Does it matter? Of course it does; such titles allow us to rip the galaxy into two halves: light and dark, good and bad. Perhaps I am neither, and I hold both as what they really are: pieces to a puzzle.
Hold until HD 4870, not really a bright idea (at least not financially) to upgrade from one high end current generation card to another high end current generation card.
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-Advocate of the 64-bit OS
-Friend of Sound Cards
-Enemy of cheap PSUs
-Fanboy: eVGA, GIGABYTE, Antec, Seasonic, PCP&C, Logitech, and Corsair.
With 4870 less than one month, I'd recommend to sell your card before its worth for price falls down further. You would probably get $100 now for it. Thereby spending $200 additional would put you on top of line with 4870.