I asked a similar question about my 8600GTS topping out at 73-75Â°C, and everyone told me that it is 100% normal, and that those are the temps I should expect with stock cooling. At the time, my idle was 50Â°C because I was going caseless (but now I get 57Â°C with a case), which again, everyone said was perfectly normal and that's what I should expect. And then I also had a lot of people telling me that it was even safe to run them at 90Â°C and higher. One guy said his card has been working just perfectly ever since he achieved something like 125Â°C. They all basically commented similar things to the effect of that GPU's were made to take this kind of heat.
So, in conclusion, I believe with my whole heart that this applies to ATI as well as I don't see any reason for them to be different, especially since you're getting almost identical temps as I do. In fact, you have a case, and you're getting better temps than I get with my 8600GTS.