If ATI sent you that card and the chips are Samsung brand I think they are for sure 2.8ns chips, anyway you can check them by the code because they have a long number and after that there's a dash "-" and a combination of letters and numbers. One of those numbers must be "2".
My 9800 PRO (arrives today but my sister sent me the code a couple of days ago) has samsung chips with the code "K4D263238E-GC2A" ...... the 2A means 2.8ns chips.
You can check the following link to check your memory chips:
What memory speed?
I do believe that since is a new card and is built by ATI it must have an R360 core, from what I've gather by reading other threads most newer ATI 9800 Pros comes with the R360 core, it's true that the only way to know for sure is to remove the HSF.
Anyway I think you should keep the 6600 GT, AFAIK is a superior card specially with recent games. Put the 9800 PRO up for auction on eBay, I got mine on ebay and paid $160 (used), most brand new ATI 9800 pro get sell for around $200. I would've get a 6600 GT, but since I'm outside the US the Newegg guys won't accept my local credit card ( and my sister who lives in the US didn't have enuff money right to spare on a vid card for her beloved brother :laugh: ), so I had to settle for anything I could get on eBay, and the 6600 GT are currently too expensive there (around $230 shipped).
Cheers