sorry Dave, but i agree with Rob on reliability, i was a big fan of ATI for years, then once games started to get more advanced i got more more and more graphics card problems, the last straw was last year, i had a sapphire 4850, which, when working was superb, but one day i fired up my pc and i got a message saying no vga hardware found, i re-installed the drivers, but again, next day i got the same message.
i took it back to the shop, they exchanged it for a 4870 cos they hadn't got another 4850, got it home, installed card and drivers, played a few games and was impressed with the frame rates, tried it later on and i kept getting the same message, vga hardware not found.
so, after a phone call to ATI they could not answer my question, so i took it back and re-installed my nVidia 9800gt, and to this day has never let me down, i get well above average fps, but i think the processor is carrying it a bit.
one day,when funds allow, i will get a new card, but for now, nVidia rules for me.