Start at 200 and go up by 10 until you start getting hardware errors then go down by 5 until you receive no more hardware errors. Not all R-Box's are the same or in the same environment. I have 4 of them running at 32GH/s for a total around a 128. I also modded the back heat sink with one similar to the front with a fan on both ends. I have not tryed to over clock it much But mine run find at the 290 clock speed. Oh also power is a factor in getting hardware errors also. If your using a power pack to run it i recommend a min of 6amp for the speed your trying. As power packs tend to lose some amps as they warm up. If you need any further help let me no.....