Set core clock speed to 1175 and memory clock speed to 1500.
You should get around 20Mhs. Also try setting -etho to 0.
Lower core clock speed if it crashes.
I did another tweak and I'm getting around 26Mhs. But need to check how stable it is.
-etho dont exist...
you say -etha 0???
im try with all freq and never get 20mhs... i set all variables and virtual memory to 16gb
1x r9 280x sapphire eth/sia
15.12 driver
win7 x64
miner v.5.3
i set 1175/1500 powlim 20 -dcri 70 = 16,9mhs/593mhs
-dcri 60 = 17,1mhs/513mhs
-dcri 50 = 16,8mhs/420mhs
-dcri 40 =16,5mhs/331mhs
*if i set low dcri hashrate low on dual miner..