The Performance Benefits To Running AMD's Radeon VII With Linux 5.0 + Mesa 19.0
Batman: Arkham Origins running under Steam Play with DXVK was faster each step of the way though it hung under Linux 4.20 with Mesa 19.0, leaving that combination out of testing. But going from 4.20 + Mesa 18.2 to Linux 5.0 + Mesa 19.0 yielded a respectable 8% increase in performance for this Git state as of launch-day.
Deus Ex: Mankind Divided benefited greatly from Mesa 18.3 and newer. Since moving to Mesa 18.3, there hasn't been much churn out of Mesa 19.0, but that initial bump was a 50% increase in performance. Keep in mind Mesa 18.2 is what's shipped by the likes of Ubuntu 18.10 and the packaged Radeon Software Linux driver, making it worthwhile at least for some games to upgrade past that stage.
DiRT Showdown also sped up a lot in going with Mesa 18.3 or newer, but interestingly some more performance was squeezed out of the system by running on Linux 5.0.
F1 2017 and F1 2018 (Steam Play) had stability issues using the older Mesa 18.2 driver with Vega 20. The performance otherwise has been pretty much flat in this case atop the RADV Vulkan driver.