cpus=1 is very stable for me.
It's not ideal though if I you can't use both cores. I can barely play 720p with one core only.

As for the multiplicator, if I change it to 10.5 what else do I have to adjust as my system does not POST on this setting.
FSB is at 200 and LDT/FSB freq ratio is on Auto. I have a 4200+ X2.