I recently bought a second-hand z420. It normally runs Windows 10 for tasks like video editing, and I am happy with it.
Its second use is experimenting with Linux. Currently installed: Centos 7. It runs but it seems to be noisier than under Windows. Since there seems to have been some Linux support for this box (see Ubuntu certification), I wonder if HP still offers drivers that I can install for better temperature and fan management.
Ubuntu, Centos or generally Linux would all be fine.