I tested with Z77A-GD65, BIOS 10.5, the other system was my 3930K with XPower 2.
On the SB-E platform, things were quite 'predictable', and the behavior of the GPU didn't change between CPU on HSF vs CPU on LN2. (Using Gen2 mode btw)
But on 3770K+ GD65, when I throw temps like -150 or so, suddenly the GPU acted 'strange', when the GPU got some errors and I restarted, the system will tell u that the GPU is missing (dE Post Code - cmiiiw).
To fix this, Usually I had to heat the GPU pot to -20 before it can boot normally again, and this NEVER happens on my X79 system.
Will try on both systems again this weekend to make sure.