Hey Andy,
yes, I use Linux and (among different distributions in the 90ies) the Debian GNU/Linux distribution since it exists without a pause, the only thing is I switched to the Devuan fork at the moment when, with Debian 8 “Jessie”, Debian made the use of systemd as the init system mandatory, and since I think systemd is not a PID 1 replacement but a disease (and first of all since they made udev now being a part of systemd, so udev would lack if you don’t use systemd), I used the possibility to cross-upgrade from Debian 7 “Wheezy” to Devuan 8 “Jessie”. I run it on most of my PCs and notebooks just as I ran Debian before. The majority of packages in the repository is of course identical (mirrored), it’s just you don’t have to use systemd, you have the free choice of the init system (Init Freedom). Recently I wrote this and it’s still valid if you’d like to try:
Linux-based systems are usually excellent to get the most performance out of aging PCs. I use FreeCad and Blender, I would suggest for CAD/CAM and 3D applications to have enough RAM. But I run them not only on my Xeon with 64 GB RAM, but also on e.g. a small passively cooled Celeron with 24 GB RAM, everything runs smoothly. I have the swap on a SSD just in case, so it is very fast.