FirePro driver 17.Q4 (2017-10-26), massive performance drop with Direct3D 11 apps

Windows 10 1709 x64, FirePro W5100 graphics card

Previously I have used driver 17.Q3.1. Just updated to 17.Q4 dated 2017-10-26 from here .

 

I noticed a massive performance drop with a couple of Direct3D 11 apps. This isn't just natural variation but clearly a bug.

 

For example, the Dolphin GameCube emulator easily ran at 60 fps in D3D 11 mode with driver 17.Q3.1. With driver 17.Q4 it runs at ~8 fps. The performance drop is only in Direct3D 11 mode; the D3D9 and OpenGL backends are fine.

 

Has anyone else seen a similar issue with other D3D11 programs and the 17.Q4 driver?