I don't know the R9 380 has been retired by AMD but I switched to an Aorus RX 570 ... much smoother gaming in Win7x64!
If your HDD is limping then you better get sumtin' decent - SSHD is minimum to keep goin'
Edit: After literally months of searching I think I have found a solution. Completely exiting f.lux solved this issue for me. Just disabling it had no effect, for some reason if I exit the program entirely it fixes the stuttering. I hope this helps everyone that has this issue as well and AMD provides a fix in an upcoming driver release to fix whatever conflict f.lux is creating.