I got 2.2 with BusyBox to consume ~2200K at boot after a lot of fiddling. Left me plenty of user space for doing command line work on my 4MB 386; i mentioned in another comment though, X was only really useful as a remote terminal in 4MB, to run a local program via X pretty much required 8MB. But pretty sure i got Doom running in X on 8MB...
I did all these experiments a year or two ago. I lost most of my work due to a hard drive failure (the one in my workstation, not the 386 lol) but all the surviving work is on my github: