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 timingBingo. Run mem at 2000 and follow the quick tut I posted on how in get timings @ 2000mhz. Other tut's available as well, just google search.