I thought it was time to upgrade the old video card which was a Power Color ATI 5770 1GB.
I had a bit of a look around and thought I'd stick with AMD/ATI which may or may not be wise but I know the issues I've had and resolved with ATI.
I looked through the support forums and settled on an R9 380 2GB from ASUS. It seems to be well supported in the latest kernels and they've developed an new driver (amdgpu vs radeon) so I'd imagine it's going to get way better over the next few months.
It plugged in easily enough (double slot sized card) and first thing you notice is this is quiet. The 5770 was noisy at idle and very noisy when playing games. I've only played TF2 but I can't even hear if the fan on the video card is going over the CPU fan now. The CPU fan is an Arctic Ice one so it larger and slower than standard and so usually pretty quiet. Downside is TF2 was more slightly choppy than it had been on the 5770 so it looks they still have some optimising to do but this is early releases of the driver for kernel and xorg. OpenGL is now 4.1 from 3.3 with the old card so more games work.
On Gentoo you add radeonsi and amdgpu to the VIDEO_CARDS list in make.conf and do a emerge -DuN @world to update Mesa, xorg drivers etc. emerge the amdgpu-ucode files and add them to the kernel and you're done.
I'll add more as I play more and as new drivers come out but so far it works and is quick enough to play games and has plenty of potential to improve.