4850s are good tractors also, but some would caution you to stay away from the ZF front end. I believe the last year of the 4850 was the only year to have the Deere front end.
What's wrong the ZF? Got a 4450 with 17,000 hrs. and a ZF.
I didn't say there was anything wrong with them. A couple of mechanics have told me parts are more expensive if needed. Hence, some people may caution against buying them.