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^ It might be that with the high CPU overclock combined with the GPU overclock things were getting too hot. If your CPU is fully stable so far now it'd be worth pushing it up a bit more before you start overclocking the GPU again.
Quite possibly yes. I've been working on case airflow too to help things. Just a pain that the H80 sits right on top of one of the boards heatsinks and no way to push air onto it.
Currently CPU is hitting 53° on the core after a good couple of hours gaming, with the H80 set on it's lowest.