Also in my experience the Win 10 would deliver 940 at those clocks with two threads. Two threads just doesn't help in linux. At least it didn't work for me.
Which miner are you using there on windows 10 to achieve 940H/s?
xmr-stak-amd.
Is it possible to share your .rom file? I also need intensity and worksize values... I'm trying to increase hashrate for a week