I've got a Rk-Box, and I wanted to make sure I have done all the tricks. I have never gotten it below 10% error rates. It seems other people have higher hash rates than I do, and that's kinda frustrating. I've used rockminer's cgminer and tried their raspberry pi image, changed around frequencies, and I even replaced their USB hub with my own (no difference).  Here's what I get:

300M Freq: 456 Gh/s, 11-12% error for ~405 Gh/s poolside
320M Freq: 478 Gh/s, 17-20% error for ~395 Gh/s poolside
350M Freq: 475 Gh/s, ~14% error for ~405 Gh/s poolside

I've played with it for a week now, and haven't gotten better. Anybody with better specs have any additional tricks? Or did I just get a poorly performing box?