Thanks for the very useful replies guys, now I have a question about frequency. Looking at the datasheet for the BM1382 chip, I see a table for typical hash rate and power, where 225MHz is 0.528 W/GH, and 250MHz is 0.583 W/GH, and 275MHz jumps to 0.702 W/GH. So, what's the sense in bumping the clock up, when the ratio gets worse on power consumption?
Wow. Those numbers are not right at all. The lowest I have ever gotten is .80 W/GH. Bitmain advertises .78W/GH. Below is my best number vs. advertised. Most of mine got between .86 and .89. With a high quality PSU running at less than 80% max current, the efficiency stays consistent (in my tests). Some PSU advertise on the box their efficiency percentages. I talked about doing a bigger study with various PSU's, but never got around to it.
MHz Avg Gh/s Watts Efficiency W/Gh PSU Model
225 453 363 0.80 1300W Rosewill Lightening, 80 Plus Gold
225 453 355 0.78 Bitmain Advertises