I ran a D620 24/7 as a server from 2010-ish to 2019. For some messed up reason i loaded it with Windows server 2008R2 or some crap like that. Never bothered to re-provision it. When I eventually replaced it with 2 rPIs, the closet where it lived dropped quite a bit in temperature.
I ran a Dell D630 for a number of years without issue.