Thats Quite Cool for a Core temp actually .. I Have a 6800 Ultra and it runs at load temp of 80c steady .. the ram will heat up to 60c..
This winter i frose my room out opening the window to -30 temps and the Core went down to 68/72 under load.. Runnung benchmarks i saw no gain or loss in Fps.. Basically it runs the same Fps at whatever heat the core seems to be at.. its not overclocked.. and i still have 3 years on warranty.. im not even remotly worried about these temps.. :} i do understand the 7800 solutions are a bit better designed than my Card, but they all have a core slowdown threshold of like 120 130 c .. heh.. so your fine .. IMHO :}
cheers