Claymore's CN miner 11.3 gives on my 270X 4Gb 550-551 h/s.
SRB max 546 h/s.
Not bad result, but Claymore's miner without fee and gives a bit higher speed.
SRB can't read hardware sensors from 270X, Claymore's do that...
Have you tweaked itensity yet?
0% fee to 0,85% fee is not such a big difference to put a negative point on it.
And SRB is still in developing, Claymore not and that is a big difference .