I did an upgrade from 1.4.0 to 1.4.2 and then to 18.104.22.168 this weekend.
It took me 14 hours in total with a lot of testing. The biggest problems I had were:
- missing tables when running the normal upgrade routines
- incorrect constraints in the database
- template issues with an old template
- 3rd party plugins that needed an update or re-installation
Overal I feel confident in doing it again it took me 2 hours in preparation in a test env. Another 1 hour in upgrading. 2 hours in testing and then doing it again from 1.4.2 to 1.7. After that I need 2 hours to get in back to the live server (a large upload) but in the end it is running like never before.
Client is happy with all the previous bugs gone but I learned 2 things:
- Test, test, test
- run it on a separate environment and upload it to the live environment afterwards
My 2 cents; I would go for 1.7 directly because 1.2 is really old....