Re: 40mm or 50mm?
I recently acquired a Leupold LRT 8-25x. Yes, it has a 30mm tube, but be aware that the outside objective is 58mm, while the outside objective of the Leupold "40mm" 8-25 is 51mm. That only .275" greater.
And, if you use the Burris signature "high" model, the lift isn't too much. The 30mm Burris high rings are actually midway between the 1" medium and 1" high. On a one-piece Leupold base, I can get a decent cheek weld on a standard stock. I've seen a lot of 40mm sitting on weaver bases that sit higher.
It's just about sweating the details and picking the right hardware setup.