Has anyone gotten a set that couldn't even do stock?

I'm sitting at 2.2V 533Mhz CAS5 unstable. I'm seriously considering of going through the hassle of an RMA. I've decided to go a different direction for better bandwidth.

@2.2V, I can do 3-3-3-9 @320Mhz 1T

But it still doesn't seem all that stable. After 2-3 days of folding, I get the the occasional restart. I'm testing at 2T now and seeing if that gives me better results.

Is it possible my motherboard might be the trouble and not the RAM? I ran the 533Mhz with a memory divider so my FSB would stay within very reasonable values (no higher than 340Mhz).