Upgrading from 3.4.2 to 4.1.1 – Ummm….

Hi there!

I’ve been given the task with updating a WordPress site for a client. However they neglected to tell us they have never updated WordPress. As such, I am looking at the awesomeness of a 3.4.2 interface. I would really love to upgrade them to 4.1.1, but I’m really concerned functionality may break, and it may create a boat load of problems.

Would anyone have some guidance or suggestion for how I can test, or make this a better transition? I’ve backed up the site, but what about going back to 3.4.2 if all goes to hell in a companion cube? I’ve never updated a site this far out of date so alarm bells are ringing.

Thanks very much!
Sara