Transistors rx480-5,700 million vs 390x-6,200 million
Bus Width 256 bit vs 512 bit
so your 480 is approximately equal to the 280x and will never reach the level of 390
So what ?
Pitcairn have 256 bit bus too, but only 100-120 H/s
Fiji have 4096 bit bus, but it does even less than Havaii.
Bus width is only part of the equation. Bandwidth is a better representation.
RX480 vs R9 390 vs R9 Fury
Frequency: 2000 MHz 6000 MHz 500 MHz
Interface: 256-bit 512-bit 4096-bit
Bandwidth: 256 GB/s 384 GB/s 512 GB/s
Being that equihash is specifically designed to bottleneck on bandwidth I wouldn't hold my breath for major increases on the RX series...
Cache size and cache bandwidth are more important than memory bw. In case if Claymore use merge sort in his miner.