Ryzen 1700/10.13.2 Build Complete - Slow GTX 1070?

I just got my Ryzen build up and running on High Sierra 10.13.2, and everything works: bluetooth, sleep/wake, ethernet, GPU.

The CPU benches right where it should: https://imgur.com/a/R7rJc

However, the GPU is severely underpowered: https://imgur.com/a/R5h3T

I see the same performance hit when gaming, Portal 2 for example is pretty sluggish at native resolution and ~medium settings.

So far as I can tell it's detected properly (the second unidentified device is my 1070 Ti which is a separate hurdle): https://imgur.com/a/qfq8V

I have inject_nvidia disabled through Clover, and nvda_drv=1 in the boot args, but these were all changed after I noticed the performance problems. And it seems to be using the Nvidia Web Driver regardless of these boot settings.

Full boot args: -v darkwake=no npci=0x3000 nvda_drv=1

And GPU settings:

<key>Graphics</key> <dict> <key>DualLink</key> <integer>1</integer> <key>Inject</key> <dict> <key>ATI</key> <false/> <key>Intel</key> <false/> <key>NVidia</key> <false/> </dict> <key>NvidiaSingle</key> <false/> </dict> 

What should I try next? I know it's not an issue with the card itself, as the GPU runs fine (at full speed) when I swap over to my Windows drive and bench it.