Interesting. I'm not overly familiar with how Ethereum handles 'difficulty' compared to Bitcoin etc - I would have thought though that all miners would be equally affected by the increase in DAG size uniformly, and thus the overall hashrate would decrease, but along with it the difficulty would drop too so it would be a net even result?

I've just started mining it myself with an RX 460 and get a hash rate of 10Mh/s - does that sound right to you? It's an MSI card.