Mauser 416, Hi.
We are adaptable creatures, but it becomes a real pain in the butt, after a while, just adapting to an extra 1/2" length of pull that shouldn't be there. It is far easier to modify the gun than ourselves.
I think that the balance point should be between the hands ( in your natural hold ) and the butt should come up smothly, from the ready position, without snagging your clothing.
Everything has to fit you not the other way around. Once you have a gun fitted to your build, you will be amazed at how less tiring shooting is.
I have an old 1917 Hollis, nitro proofed SxS 12g hammer gun,that I wouldn't trade for anything because it fits me exactly and did from the first time I picked it up. When I bring it up it is there, on target, every time. It's just up to the nut behind the butt to slap the trigger at the right time.

As Bramble says, the time and money getting a gun fitted is well spent.

Cheers
Afro