I don`t know how exact you can adjust memory access to GPU memory, but ppl that compare and cry here thet RX 4xx should be fast as 390x should first learn that any architecture is different, the driver is accessing GPU memory as best as it can, if zcash need many small accesses and if 256bit bus is not wide enough its logical that 384 or 512bit bus will be better
Fiji should be faster,but maybe code isnt be suited for HBMi feel 280x the cards Claymore loves the most - will have 200 sols per card i nthe update 
)
)I like 390-390X the most - I'm going to reach 300H/s on stock clocks.
RX480 will show about 190-200 I think.
280X - about 200 or a bit more.
Yes, but too wide memory bus, 4096bit is too much for most PoW algos and therefore cannot be used completely.
Nano will show about 250H/s, may be I will reach a bit more.