I think I am getting closer.....
I tried the GTX460 today, and had many issue with this thing turning off, restarting, etc.
The bad news - this tells me the mobo was not the issue. This also tells me the GPU was most likely not the issue as two different ones are causing strange behavior.
The good news - my new power supply is on the way, as that is the only thing I can attricube this odd behavior to. And, if this corrects it that means I will then have a spare mobo and a spot for one of these extra GPU's. Once I can find a steal on an AMD processor or something AM3+ socket type to power it all.