I love the Elite 4200s but they have less eye relief than some other scopes. I have a 7mm Ultra Mag with an Elite 4200 4x-16x-50mm and the scope never touches me. As such, the 300 Ultra may or may not be fine with the Elite.
The thing about Leupolds is that, like most scopes, the eye relief is variable, not fixed. If you shoot at lower mangifications, then you have a lot of eye relief. However, if you shoot at high(er) magnifications, then the eye relief is about the same as the above mentioned Elite which has a fixed eye relief of about 3.6".
Zachary