Thanks for your reply!... yeah, i read "-h   number of hashes that GPU processes during one round. If not specified, default value is used. For many cases you can increase performance by adjusting this parameter value. For example, "-h 832" means HashCnt=832 for all cards. You can also specify values for every card, for example "-h 640,832,1376,0", zero value means autoselection."

When looking into Core/mem frequencies, I fully understand the physical implications of parameters like mem speed, noise, power and frequency... and the implications of those variables on some miscalculations that lead to an error. But didn't get what this parameter does at low level... what's a "one round"? The hashes take always the same time to process? Difficult don't make it more difficult to processed it?

Thx!