I just fired up my Firepro s10000 it's getting an excellent 779kH/s with stock clocks, however it has the same issue as the R9 280x's. This is in my main Ryzen 7, 16gb system, so it can't be a system issue.
Is it crashing after a while? or crash at startup? Are you on the latest adrenaline drivers? Crimson drivers have issues. Also some pools are crashing the miner more often than others. Wich pool are you using.