I've had the luck to snipe a 9070 XT at a sane price on launch day and I've been using it on Linux since it arrived yesterday so I wanted to share some words, mostly praise, about my experience.
I'm currently on CachyOS with linux-rc, mesa-git and linux-firmware-git and the experience has been amazing. The occasional driver bugs exist, especially when using raytracing, but overall it works really well.
I've ran a few benchmarks and in rasterizing I always get really close to the Windows performance, e.g. Cyberpunk 2077 Ultra (no RT) gets within 95% of Windows with similarly good frame times. Cyberpunk's Raytracing can cause a crash and when it works is only about half of Windows performance with very fluctuating frame times, but other games like Control or GTA V Enhanced run very stable with max RT.
Another selling point of RDNA4 for me was the efficiency after I had returned my 7900XT card in part due to super high idle usage (80W+) on Linux. Here on launch day it's using 40W with my setup which is far off the <10W that are possible according to Windows reviews but already a lot better than the previous generation.
(Update 4 days later: Getting as low as 4W driving two 1440p 144hz screens on latest drivers, even lower than Windows, nice stuff.)
In games the efficiency is incredible, the card basically runs any game released before 2021 at max settings in 1440p with a 144 FPS limit, only drawing 40-110W which I assume could be even further reduced if the base usage is optimized in the future.
Lastly, VR just worked out of the box which impressed me the most. I've tried Vertigo Remastered which runs through SteamVR+Proton and I've had zero issues, I put highest settings and played through a whole chapter with no stutters.
A huge thanks to the developers who worked towards making the launch experience as great as it is. I've been on Linux since 2017 and it feels less and less like being a second class citizen thanks to these efforts and especially Valve.
I really like this visualization of that concept.