That's definitely on the hot side, you should aim to keep it below 80°C, 85°C max. My HD 5870 runs at 81°C when mining at 915MHz, the fan is spinning at only 33% speed. Try cleaning the heatsink, there is probably a big wall of dust right where the fan blows the air into the heatsink.
I have my fans set to be at 100% if it hits 60oC... Some people say all this junk about fans dying so easily if they're at 100% constantly, but I've had 5 fans die out of ~15 cards running non-stop for the last 10 months.... you can always buy a replacement fan for $10, too.
all the rejections cause of p2pool. that card is running at 50oC right now... but just because it's in like 40o ambient temp =p
i don't like it when my cards go above 80oC. that includes any of the GPU sensors... if you don't have a good thermal paste job, your main sensor could read 65oC, but you could have another sensor at 85oC.. i've had a few like that that I've gotten from ebay. you should get those all within 10oC (ideally within 5oC)... the VRM temps, I don't like them being above 100oC, but it doesn't BOTHER me until they get to 110oC.