My rig consists of 2 x R9 290X and 1 x 280X. I'm mining with Claymore's ZCash AMD GPU Miner v12.5 on Debian GNU/Linux. I'm getting those numbers:
ZEC: GPU0 334.327 H/s, GPU1 295.035 H/s
GPU0 is a 290X, GPU1 is a 280X. Comparing their firepower I'd have expected much more H/s with 290X than with 280X... any explanation to this behavior ?