I have a ThinkPad T420 that is sufficient for most tasks that don't involve HEVC acceleration. It's got a mobile Sandy Bridge i7, booting off of a SATA SSD.

The only thing that really needed an upgrade was the display. I ditched the crappy 1366x768 TN for a 1440p IPS and an LVDS-eDP conversion board. Looks fantastic. Runs great.