just wanted to pitch in a datapoint.
benched air for a few days at ~1.4vcore, 1.6~1.65 QPI/DRAM (VTT), and 1.6-1.7 vDRAM.
DI bench session on friday at ~1.6-68vcore, 1.75 QPI/DRAM (VTT), and 1.65-1.75 vDRAM.

Back on air now and behaving as well as ever. Interestingly enough my Kingston hyperx 2000mhz kit XMP sets QPI/DRAM to 1.65v automatically; which will get uclk up to 4300 on air, 1.75 is good up to 4500 and maybe higher.