Oh ouch. It's good to hear that your normal motherboard is fine. Do you think that you might have overloaded or overheated something on the motherboard or was it a manufacturing defect?
I still think that an ultra-high LLC at anything less than 4.9 GHz is indicative of a poorly optimized OC (or possibly of a motherboard with very weak VRM phases).
I didn't mention that in my above posts, because most enthusiasts get motherboards with high quality VRMs (like our asus boards). But even reputable companies can sometimes have a product ship with weak components.
It was defective, the day I got my i5 it randomly shut down without any overclocking at all, then it did it again today under no load.
Two of my cores are at 5.0, one is at 4.9, and the other is at 4.8, so Ultra High LLC might be justified, but I am going to try High LLC overnight, and maybe 1.395v.