RX 580 8G, Hynix memory (2225 MHz IIRC). I'm pretty happy with the speed, yeah. I reach 31.6 MH/s per card with a clock of 2250 MHz but shit happens from time to time (although my memory errors appear to be very very very low).
Care to share your config file (memory and core speeds and voltages) ?
What's your per gpu consumption?