wow my 470 only gets 575 h/s, are you overclock the memory??
your mobo and cpu support pci e gen 3 ?
i am using an sapphire rx480 4 gb on pci e gen2 and he got same speed like you because this a nice bottleneck
not possible there is no bottleneck with pci-e lol
you aware that we run the gpu on a pci-e 1 x with riser lol
i run for long time a r9390 on first generation pci-e with atlhon 3200+, was working just fine
if you only have 575h/s, you just have the wrong memory timing