I'm getting ~32-36 MH/s while with NicehashMiner soft 42-47 MHs on gtx1080.

That is interesting.  I get right about the same for both when I randomly check, maybe .25-.50 a day difference.  Being able to cash out into paypal or bitcoin when ever I want far outweighs any small nuance.  For example, when bitcoin drops, I can cash out into bitcoin.  When bitcoin is up, I just keep my balance in winminer.  I can just keep buying dips.  With nicehash, several times bitcoin dropped when I got paid out which lowered my profit for the period.  You can make quite a bit by just buying the dips, far exceeding any fees charged.