My 806mv cards may be golden samples (or at least silver,) but i have 5 of my 64s online now, at 806, 806, 812, 818, and 825mv.  Effective cclock is between 1150-1190, and reported h/r is 19.53-19.54.  I'm pretty sure you could get any 64 to 806 if you drop the cclock low enough (which is reasonable on this algo,) but it seems anything under 1200 MHz shouldn't need more than ~825-831. 

Even sub-1400 shouldn't need more than ~850mv, so it seems like you most likely have a problem in your ODT profiles or ppts:

1. Check that you're SOC is running 1107 and not 1200.  I assume it is, since you say your cards crash above 1107, but SOC is the primary reason i see jumps from sub-850 to above 875mv.

2. I've noticed in my testing that I can have cards crash if lower states aren't sufficiently powered - seems they can trip up during the brief transition across states during miner startup.  Solution is to either disable all lower states before starting the miner, or carry your top voltage all the way down to at least p2 (if you're using super low voltages like me.)

3. I have no definitive proof, but I have gotten the sense over many tests that the GPU threads aren't super isolated - i.e. one GPU struggling w/ insufficient power may cause another GPU to crash first, making it rather difficult to determine where your problem really lies.  Even if it's not necessarily the case, it's good practice to tune the GPUs one at a time - only adding another to the list once you've ensured stability of those already online (over hours, not minutes.)

Lastly, i should mention i'm on Sapphire Nitros, though i do have a single ref 64 i have yet to switch over, but which has always performed within the top third performance-wise of my nitros, so I don't think there's a inherent difference, other than cooling design.