You could also try setting custom intensities for each card, separated by commas (-I 13,13,19,20). You can also use commas on other settings. I don't know the max temp of most of yours, but I do know r9 cards can take up to 94c and be ok (I keep mine at 85-88).
Intensities are already separated by commas

Cheers guys, I may have a play around when I have some time then.
One last suggestion, make sure the clocks are stable and not fluctuating a bit. Low watts can cause errors. I turn my 290x power limit to +10 when mining, and get as low as .5% rejected on some pools.