It does happen however, on the machine I benchmark, after about 10 minutes of running at full speed. Take a look a the included .eps file. This is simply a run of 200 identical tests of my fastest SSE2 double precision code. I have repeated the test several times, and I get the same result every time. I have tried inserting a 4 seconds pause in between each test, at it solves the problem, so I see no other logical explanation that the thermal safety device in the chip.
First column is seconds, second column is mflops.
If you have gnuplot installed execute 'gnuplot gnuplotrunhot' and look at runhot.eps Cheers, Peter.