When it comes to mag wells on remington 700 long actions, there are 3 predominate layouts.
Remington Long Well
Is the standard well that is in most Remington Long Action 700's. It is perfect for a 7 STW, 7mm Rem Mag, or any other heavily tapered case.
The Wyatt Long Well
This well is a custom well that many custom 700 clones have. It is lightly longer and a touch wider for some of the more modern magnum calibers.
The Wyatt Ultra Well
The Ultra is a perfect fit for the 28/30 Nosler, 300 Ultra Mag, and other oversize cases.
Note: all the wells will work with any of the cases listed with proper gunsmith fitting. The only one I would really recommend is if you want to run something based on the Ultra Mags, these actions aren't your best choice. They will work, but will require lots of fitting.