Windows 10 vs. Linux 4.15 + Mesa 17.4-dev Radeon Gaming Performance
Lastly for this Vulkan racing game, when pushing it at 4K with medium image quality settings, the Linux performance was similarly lower when compared to Windows. The RX 580 was under a 60 FPS average while the RX Vega 64 did manage to still have a minimum frame-rate just above 60.
With another more mature racing Linux game port, GRID Autosport, that uses OpenGL, the Linux performance on both the RX Vega 64 and RX 580 were both significantly lower than Windows 10 with the latest Radeon Software driver. In fact, the RX Vega 64 on Linux was only as fast as the RX 580 on Windows.
Shadow of Mordor at 1080p with ultra image quality settings still showed a significant loss in performance when using Ubuntu 17.10 with Linux 4.15 + Mesa 17.4-dev compared to Windows 10 FCU.
But when pushing Shadow of Mordor at 4K, the RX 580 now performed close to the same between Windows and Linux, but its minimum frame-rate was significantly lower with Linux and the average frame-rate wouldn't really led to a playable gaming experience. The RX Vega 64 meanwhile was still noticeably slower on Linux.