The RadeonSI/RADV Performance With Mesa 19.1
DiRT Rally 2.0 running on Linux under Steam Play did appear to be up ever so slightly with Mesa 19.1-dev for the Polaris and Vega graphics cards tested.
F1 2018 as another Steam Play title didn't see much change with Mesa 19.1-devel but its performance is awkward with the RX 590 pulling out ahead of the RX Vega 64...
Hitman 2 as the other Steam Play title tested didn't see much change but if anything the RX Vega 64 appeared slightly slower on Mesa 19.1 in some of the configurations.