after about 24 hours of test, I find 0.6 gives 0S/s for some of my cards more often then 0.5 which is never 
,
so switch back to 0.5 for now
plus, all my GPU usage is around 78% up and down, none of them is reaching 100% like mining other coins
, so switch back to 0.5 for now
plus, all my GPU usage is around 78% up and down, none of them is reaching 100% like mining other coins
For the 7970/280x, the GPU usage is about 85%. For the newer 390 cards, the usage is about 100%.
so does this mean the miner is not fully optimized for old GPUs?
I think the miners are not fully optimized for all GPU. For the new GPU such as R9 390, only 30% of the memory load.