I would like to bring this topic to top as I have a common problem.

I use RX470 and RX480 on stock settings (C1270 M1750) with Nicehash -> Claymore miner.
RX470 shows 17.7 MH/s in "Standart" benchmark and only 15.8 MH/s while mining.
RX480 shows 25 MH/s in "Standart" benchmark and only 19 MH/s while mining.

Tried to run "Precise" benchmark.
RX470 showed 20.9 MH/s in benchmark, still giving 15.8 MH/s while mining.
RX480 showed same 25 MH/s in benchmark.

Tried to run a single Claymore miner - same mining hashrate.

I know that RX470 should give something about 20 MH/s by stock settings and RX480 should have 25 MH/s.
Power is absolutely more than enough. No throttling noticed in MSI Afterburner.

Hashrate for Equihash is the same in benchmark and mining, so I have to run both cards with equihash getting lower profit.

Many thanks for any ideas...