Hi, here's the current "state". Switched to kernel 2.6.29-r5 (genkernel) and (gentoo) stable nvidia drivers. No change, System freezed anyway.
I re-checked the memory manufacturer's commendation about voltage (between 1.7 and 1.8 Volts), and changed from auto to 1.71V.
The sys is up for 7.5 hours now at nearly the same workload then before, no faulty behaviour so far .... hope dies last

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Funnily enough, "free" shows much lesser caching then before (I did forget to mention that I had heavy memory consumption and quick rising "cached" value. I have no idea if this was a kernel issue or was mem related (my other systems : 2.6.29x gentoo, 2.6.2x kubuntu both amd64 as well) did not show such a behaviour, never ever.
As for temperature sensors, lm_sensors (sensors-detect) marks the CPU temp sensor as "to be implemented", so there is no way to totally eliminate overheating. I found a kernel patch activating the support, but at this time I'm not willing to risk more instability.
I'm curious if the machine will be up tomorrow morning or be freezed .... Thanks for all replies so far, I hope I can stop bugging you with this problem soon
