I am using CPUminer (GC3355 fork) with this command line:

--gc3355-detect --freq=800 --gc3355-chips=400

Avg in Minera shows 26.66Mh/s. Pool shows 26,815 Kh/s, so I think it is accurate. I also have the miner restart every 24 hours as I do see a drop in speed over time. This seems to help keep the speed consistent.

I do run the Gridseed 5 chip units at 850, but that speed gave me less Mh/s on the G-Black.

In case anyone is interested, I have also modded my G-Black by replacing the three 80mm x 38mm fans with two 120mm x 38mm fans. Runs just as cool with a much more tolerable noise level.

- fvineyard