I have 830H/s with RX 470 with 150W at wall for whole rig.

if he's going with the stock settings this is normal...unless you end up modding the bios

>As i said before, with those low temps, i know this also could go a lot faster. Energy usage confirmed that.

The bottleneck of CryptoNight PoW algo is that it requires loading small data blocks from random memory addresses, a lot of times. Because addresses are random, memory cache is useless. You see low temps because GPU core does not work all the time, most time it waits data from GPU memory due its latency. And it cannot be optimized because the algo was designed to use memory latency to be asic-resistant. Fury X has 4096 bit memory bandwidth, but it is useless for this algo because big bandwidth is not related to memory latency.

I have a 6990. Use drivers 15.7

And mine ETH with it with his miner software not ZEC. ZEC will run at 2Sol/s per core so 4Sol/s.

With ETH you will get 13MH/s each so 26MH/s total. Almost the speed of RX480 & 390 just uses alot of power.

You can also undervolt them to like 1.0V to save on heat and power.