1. Core Clock(Mhz)
2. Memory Capacity
3. Stream Processors
4. Memory Speed
5. Memory Clock(Mhz)
6. Process:(xx nanometers)
7. PixelPipelines
8. Memory Interface: (128, 256 Bit or higher)
For Zcash I believe Memory bandwidth mainly
RX 480 256 GB/s
R9 390 384 GB/s
Secondly the Core Clock
The microprocessor gives energy perfomance.
Anyways someone can add more info..
Regards
that pretty much sums it up.. the memory STRAP comes in to play also but was not listed in original query.
Process (xx nanometers) is just the manufacturing specification.. the more advanced (lower number) processes may allow for higher core over clocks but generally it just means the chip is more energy efficient.