I'm typing this on Linux Mint, but have used many different ones. I do recommend getting fast storage and lots of RAM, so you can run stuff effectively in virtual machines. They're especially good at evaluating different distros and desktop environments/UI toolkits, not to mention testing stuff (since one can checkpoint a virtual machine and revert back to that after testing something, without having to worry about "cleanup" or uninstalling stuff). Also, they boot/continue in seconds, so even though it isn't on bare metal, it's close enough for me to not notice the difference (except maybe in some very specific cases).
For me, the motherboard is a likely candidate for replacement. By having future-compatible components, I can upgrade the motherboard if need be. Or, get another compatible CPU and motherboard, and do a cross-swap, getting a second machine.
As to what is Linux-compatible, nothing beats a real-world test. Then, one just needs to remember that Linux distributions do not necessarily run the very latest kernels, so testing more than one fresh distribution is a good idea.