mine 7970 runs bf3 like 55-60 fps on ultra and multipalyer ... only problem is karkand maps .. there are some 40 fps drops but it's fine for me ^^ metro 2033 runs on 40-50 fps i ahve to test on crysis to
80C is warm, but fine. You have about 15-20C before you hit the thermal limit.
As your GPU fan and heatsink and your case and fans get dustier, you'll see hotter temps. I like to do a complete teardown of my system every year and blown out the fans and heatsinks every couple months to make sure things stay cool.
I can't find any hard data on the thermal limit of 7970 right now, but I believe it's around 100C. Anything below the thermal limit is OK. At 90C I'd be looking for ways to lower my temps (cleaning parts, improving case airflow, routing wires), but getting that hot won't hurt the card. 90C new will quickly approach 100C dirty where it is dangerous for your card, so it's still a potential issue.