Oh, thanks! I know this straps...
Meanwhile, doctor83 released new version of his miner... Wrote that he did stable high heavy algo speed on RX 4xx/5xx cards supporting latest drivers. And he stopped to use binary kernels as before he did, and new fast kernel compiling... All as on JCE miner... After my work would try his miner...

On JCE sync version I can't still recieve stable max speed for a long time... Increasing core and memory voltages didn't helped. Lowering multi_hash parameters also didn't helped. After 15-20 minutes speed can be max (but not always), but after some time it start to fluctuate and drops to about 1 kh/s.

EDIT: Wow! doctor83 made it! His miner last version have stable speed on heavy algo as rock! And on heavy mode 3 only a bit (about 10 h/s) slower than JCE. But his devfee 0,85%... So... If I can't recieve stable max speed on JCE, I would forced to use his miner...