The limitation on the GP is going to be the thin forcing cone and we don't have an official ruling on that yet. Which is surprising because they've been out for over a year.
I agree with the forcing cone being the likely weak link, but why try to “magnumize” the GP100? My 3” has been shot a lot with the Lyman 429421 at a little over 800 fps with no signs of a problem. A fun to shoot load that will do all I need to do with a short barreled 44 Special. I’ve got Redhawks if I need a “magnum”.
