I've been on a folding team that highly encouraged overclocking. But the hard drives I used were not compatible with out of spec VIA chipset overclocking. The performance gain was small.
If your performance gain is small - and DF proves that your system is not reliable at the OCed speed - then why OC? Perhaps visiting one of the hardware sites will get you in touch with folks that have experimented with the Asus nForce2 MBs that can suggest how far you have to relax your memory timings or step back the cpu OCing to make it reliable.