I had a sapphire 4850 (single slot version, very thin, and crappy cooler, also heatsink not real copper, its aluminum painted) not too long ago, and was getting pretty much the same temps. I tried taking it apart and reapplying AS5 on it, it helped a little, but the thermal pads just didn't do their job on the ram as well after this.
I found a great deal on an accelero s1 rev2, $25 shipped. After installing that cooler, the card was 80C at load, and that was with no fan, just passive cooling overclocked too.
The accelero was great since it came with arctic cooling's own thermal paste already spread in just the right place. I didn't have any problems with the ram sinks not sticking as some people have, but I did clean the ram chips real good before attempting to stick the ram sinks on. The PWM sinks that came w/ the cooler were crap though (i think PWM chips just had too little surface area to stick), and I ended up sawing the PWM section off the stock cooler (which just happened to have both screw down holes on it). The PWM sinks that came w/ the accelero actually turned out to be just perfect for the PWM on my motherboard... go figure.
just found this salehttp://www.superbiiz.com/detail.php?p=F ... 9b9b66a600