It has already been stated in various threads about the 5800 series that Furmark is not the best test for them, haven't heard about OCCT being bad though. Personally, if it passes the benchmarks without artifacting and I can play games for 3-4 hours then I consider that stable. OCCT, like Prime95, is good to test your CPU for stability, but stability is in the eye of the beholder so to speak. If you are trying to test the temps, run multi passes of 3DMark06 or Vantage of the GPU only tests and that should give you an idea of the temps you will see.