Has anyone upgraded from 3.x up to 5.x when running OSPF or from 4.x to 5.x
I have some MT's I am using as an OSPF router and haven't upgraded them, but would like to.

Currently we have over 100 Mikrotik routers running the latest 5.5 Firmware with no major issues. We went from v4 to v5 with no issue. I'm sure you remember but don't forget to make sure you do Routerboard upgrade

Current models we have ospf running on: (all v5.5)
433
433AH
411AH
493
493AH
450
450G
RB1100
X86

Regards,
Josh