Thanks for the suggestions.
The problem appears to be temperature related:
SpecviewPerf crashes the machine if you run it twice within a short timespan.
I've removed the side-panel of the machine and
there is no problem now with either driver.
Time for yet another case-fan...
here are the results for those who are interested
[Athlon 1533MHz,MSI KT266a,Asus V8200,
1280x1024@85Hz,RH 7.3+Kernel 2.4.18-3]