Ok guys i have a solution to make it clear, let's talk about hashrates and power consumption.

My testing Rigs (2 rigs with exactly same config) :

• 6*Rx580 Msi Armor 8Gb (Samsung memory) with celeron and other low pow shits.
  

With 33b2 here are my rates on heavy algos :

• 6960 Kh/s for 750W at wall

Very stable, it can run days without crash or fluctuating hashrate. On pool side

What about you ?

I tried again and again with b5 and b6. Never got same exact hashrate for hours and thebest i obtained was 7200hs, so with the higher fee it is better to get the stable 6960hs. I hate those versions (too long time testing for nothing )