Doktor, what can you say about the random hash rate?

SRB does get the best hashrate, and I even managed 1000 mh/s for all my cards, in one run, but what happens is this:
e.g. Sometimes, GPU0 gives 920h/s, sometimes the same gpu, just by restarting miner, gives 1000 mh/s, but then some other card, e.g. GPU5 which gave 1000mh/s, may (or may not) do 920-940 mh/s.. The total may vary +/- 800 mh/s, and it doesn't change much during the run (it gets stabilized in a few minutes, stays that way)

Sometimes a gpu gets 0 hashrate, I restart, it fails on compilation phase. I use XMR-Stak to get it working back, switch back to SRB and it begins working (SRB cannot get it unstuck however many restarts!)