R9 285 Support 3840 x 2160 in VSR but R9 290X only 3800 x 1800 ? in latest 15.7 Drivers ? why is that ?
So far VSR is based on the hardware scaler which means 290X does not support beyond 1800p at this time. Only way to get 4K VSR is by using GPU based on GCN 1.2 (285,380, Fury and Fury X). Maybe in the future we might get software implementation.