Right, those are good numbers for the price, comparable to the 1080 Ti, so this bodes well for using them for mining... however we will have to see if there are any gotchas (the access patterns for mining are different than for games, so for instance GDDR5X was less effective than GDDR5 despite being theoretically faster.)
Was that due to increased latency?
That would be my guess, that the bandwidth was very high but the latency was higher than the cheaper part, maybe not all the time, but in a way that affected this hashing algorithm.