I just bought a loaded, refurb HP Z840 for $2K and I added a Nvidia RTX2060 Super, (I'd go with a RTX30XX card now). RTX's aren't officially supported though. There's some Quadro cards out there if you want to be on an approved box. Check out Teksavers, 512-6 63-5764. The Z840 is a nice upgrade from Z400 or Z800s. They have a configuration