Let it run for a while! On rx580 the difference is 950 Claymore to 1050 SRB
Have you tried use T= 1/2? and W=8/16?
I runned for several minutes. How much it must be run to achieve max speed?
T - 1 slower, W=16 didn't tried, but I don't think that worksize on 270X gives any difference.
On RX 580 8Gb I use GGS - it gives much more than Claymore.
What parameters is best for 580 for SRB?
Well, yeah, i don't know, because i don't have a 270x card xD.
It deppends i'm using I=58 , W=16, T=2 on 6 MSI ARMOR 580 8G (Micron) and got 1050+ on each.