This is what I've found too with dual mining. 11.3 or 11.4 you have to slow down the cards to get stability but still 4% incorrect shares.
With 11.0 I get slightly slower speeds vs the same card speed but I can turn them up more with stability. I dont have any incorrect shares so far a couple hours in. The effective speed is much higher.
The incorrect shares is due to the speed boost claymore did, claymore increased memory intensity for the boost and now to make it right people need to reduce their memory clock speed.