strange...
I have about 15 with 650FF firmware with the LPM fw on top, and highest i can clock them is about 668Mhz. Any higher and hashrate starts to drop.
Also i have 4 that are situated in a colder area, and they are so picky they wont even take the LPM mod; too cold, hashrate drops and they run stuck. Reboot and they go for some hours again. New flash with 650 (or autotune only) and they're fine...
So, temp. has a big influence also... Chip temp of 40 degree centigrade they don't like at all...
I agree, when too cold mine tend to be moody too, which makes no sense to me since heat is the enemy or so I thought. I think I could potentially get better results if I had the beefier PSU, I am running the 1600w one from bitmain on a dedicated 30amp 240v circuit, so I have plenty of power from the wall, but I think the PSU might be my limiting factor.