Started off shaky but overall I'm enjoying my switch to team red. My current setup is as follows.

OS: Antergos
Kernel: 4.12.0-amd-staging
GPU Drivers: amdgpu
CPU: AMD Ryzen 7 1700 @ 3.6 (factor wraith spire and no change to multiplier)
Video: Radeon RX Vega 64 LC
RAM: 16GB @ 3200

All crammed into a Phanteks Evolv Shift (if you want a complete parts list let me know, and I'll provide one.)

At the start, it took a bit of messing around to get the system stable. Part of the problem was a faulty brand new power supply that was unable to power both rails for the video card so anytime the card is pushed the system would shut down. On the Linux side of things it was dated information that proved to cause me problems, typically information that's a month old is okay, but with AMD's new CPU and video card updating every week I found my self-running in circles.

To make life a little more comfortable, I went with Antergos as my distro instead of Arch Linux as it allowed for thought free reinstalls during my troubleshooting. Now I can say that I know what's needed to get up and going on Arch so I'll be switching at some point (might just wait until 4.15 releases.)

In short, if you are using an Arch-based distro you'll want to get or build an AMD staging kernel and stick with amdgpu and mesa (no need for git or a unique build as they have the needed drivers now.)

I booted up Antergos normally (no multi-user.targer modfier to grub); this will take you to a black screen if you're using an RX Vega. So at the black screen press Alt-F2 and login

Add Kernel Repo
Edit: /etc/pacman.conf
Add the following to the end of the file:
[mesa-git]
SigLevel = PackageOptional
Server = https://pkgbuild.com/~lcarlier/$repo/$arch

Force refresh
sudo pacman -Syyu

Add the kernel, header, video drivers and Vulkan if you plan to use it (note mesa works fine I just chose to use mesa-git)
sudo pacman -S linux-amd-staging linux-amd-staging-headers mesa-git lib32-mesa-git xf86-video-amdgpu vulkan-radeon lib32-vulkan-radeon

pacman should automatically run: mkinitcpio -p linux

I use Grub, so my next step is updating Grub

sudo grub-mkconfig -o /boot/grub/grub.cfg

Then restart
shutdown -r now

Select the correct kernel (for Antergos you'll need to go down to alternatives, you can edit Grub if you want it as the default kernel. I want to keep it as an alternative as 4.15 is in the works, so I left it alone.)

Enjoy

So far I've found the RX Vega 64 LC using the opensource drivers performs well. I had a Nvidia 1080 FE card before and gaming I don't know notice the difference.

One feature I do like is that AMD has a TearFree option which is impressive! As I have a G-Sync monitor (due to once using a Nvidia card), I was worried I'd be stuck with horrible tearing but once I found and enabled this option all was well. Zero tearing and no noticeable reduction in performance. Just wow!