Got my unit this week, really a great piece of hardware! So far I am happy with it, have it running for now at 2.1Th/s with 550MHz for about 24 hours, with the flat side of the voltage knob pointing to between 9 and 10 (clock).
Interesting; mine dropped a bit down to 2.1Th/s over the last 6 days. I am still on 675MHz. It started at almost 2.5Th/s. Did anyone else experience such a little bit of drop-off after the first few hours of operation?
My only theory right now is that they get slower as the heat up and the heatsink becomes fully soaked. Not sure about that, though.