Right now the gpu for mining are 1070 and 1080 from nvidia and Rx 570 and rx 580 from AMD. They have a god ratio for performance/cost. I have tested R9 390 that has 31 MHS but the consuming is 330kwh.
And it's not melting down?
8-P
I'm actually assuming that was a typo and it's eating 330 watts, which would be in line with my R9 290 cards mining ETH.
At CURRENT pricing, the GTX 1080ti is the overall best card for ZEC - but if 1070 and 1080 pricing drops back to where those cards were at 2 months ago, it becomes a "more or less tossup AT THE RIG level" competition again.
Before the recent "shortage price gouging", all 3 of them were capable of achieving better than 1 sol/s per $ (NOT counting the underlying MB/RAM/CPU/etc) and fairly close to that counting the entire system with careful shopping for a low-cost system.
At current pricing, the RX series has VERY POOR performance/cost ratio - they were very good 3 months back before the shortages drove the pricing up though.