You figure the 9070 just has that much extra longevity here, or just that much more power?

As always, it is price dependent; the 9070 series is a decent jump from the 7800 in a few areas, so if it is within say an extra $50 I'd consider it. The XT model is only like 5% more performance on top of that as well.

Really appreciate the distro advice as well. I haven't had a home linux since whatever version of fedora was around like 15 years ago.

Happy to opine since I have been on the Windows > Dual boot > full Linux journey myself in the last couple of years. Regardless of distro, you're in for a treat; any of the modern distros are pretty good now. I'm a KDE Plasma stan as well, but thats a personal taste thing haha

Looking to do some gaming, but don't really care about it being ultra settings at 100FPS. Mostly single player stuff and do appreciate it looking pretty though.

Definitely spend the extra for the 9070 then, price comment withstanding, as it will last you awhile.

Also looking to do a bit of dev work. Usually running IntelliJ or whatever other Jetbrains product fits the language I'm working in.

I don't do much coding these days since I stick to my crayons, but looks like most of these are cross-platform. It's also worth mentioning that there are plenty of cool tools like Distrobox as well, which allow you to easily run any Linux distro + toolchain as a container to provide a sandboxed, mutable environment, so immutable distros aren't a dealbreaker either.

This is why I like Bazzite so much for dual use, because if you are at all gaming, all of the baked in QoL features make setup easy when I have had many issues with other non-gaming distros in the past, and the rest has tools to make it work somehow. Immutable distros mean you can't really screw up the OS either.