Try to set -gt for rig 2 manually the same as on rig 1.
Maybe the problem is that on rig 2 cards with worster memory than on rig 1...
Cards from the same batch. I used the Claymore for more than a year, until it stopped working, there was no such problem and the speed was 30Mh+
After set manual -gt on rig2, speed has not changed in any way
Cards the same all? It's very strange... Rig 2 take more power but speed is lower... Windows and drivers the same too? Video bioses the same on rig 2?