On version 4.7 set -cclock to 1100 and -mclock to 1500, hash rate around 20.5 MH/s
On version 5 same as above, hash rate become 21.5 MH/s
That is weird since OpenCL code was not changed. But see below.
There is some small trouble, on first run the hash will not increase to 21.5MH/s instead only 20.5 MH/s. Atitweak showing that the clock already set correctly.
I need to close and rerun claymore for the second time, then it will increase to 21.5MH/s
I can confirm this issue with 380X card and Windows rig. For my case I do not restart miner, but instead just change clock options using Afterburner once, and immediately set them back. And hashrate jumps up by 1MHs exactly as you tell. I remember someone already wrote here about such effect. So you may as well try to change clocks twice using atitweak with some delay in between. Maybe it helps.