All of my rigs run Folding 24/7 (6 rigs and 1 laptop - so far) and I can assure you that Prime stability is no assurance that a machine will fold successfully.
I have had a rig (opty 170) prime stable for 20 hours only to fall over within 2 hours Folding. In contrast, I have also had a rig (X2 4400+) fail prime in less than 1 hour but fold flawlessly for months at the same overclock.
Like The Asgard, I tend to prime my systems for a couple of hours to get an idea if it is stable or not but I never assume that it is stable until it has folded for a couple of weeks without issue. If it fails prime, I will still try it folding to see if it works.
I'm not saying Prime is no use - it has it's uses, just that I would never trust it 100% to say whether my system is stable or not.
Stan
Edit: Nice oc there btw The Asgard - great VFM little chip you've got there