I have R9 290 and RX 480. It have same problem
I try any method and driver to fix this problem,But not work
Freesync (75Hz) : on > Lag and Low FPS only around 40 because 0 % VGA loading
Feesync : Off > No problem now
I waiting for fix problem with new driver since last year please
please pleaseeeeeeeeee fixxxxxxxxxxxxx before i'm rage and buy nvidia and never buy amd again.