In the pictured setup any reasonable caliber is possible. Plus a couple of pushing reason calibers like the 338 X 378 or the 510 Rogue which is based upon the 460 Weatherby case. Very shortly this center grip setup will be carrying a 338 Edge barrel.
I carried a rifle for many decades and can say that carrying a rifle through the Alders of Alaska is a pain and very tiring. Carrying a handgun with barrel shorter than ones head and in many cases shorter than ones shoulder and the grip is nicely tucked under ones elbow is not only none obstructive, I never know its hooked on my pack upright.
I have a friend that has been diligently learning to shoot long range for a couple of hunts coming up. With his 7 WSM at 7oo yards the shot on anything is a gimme. He is hitting a softball size target every shot.
Since I have had to deal with very large bears in the flat country mostly for the past 30 years I have adopted three schools of thought over the years. Roy Weatherby and others thinking regarding.
1. Fast bullets and hydrostatic shock. Plus the advantage of hair hold flat shooting capabilities.
2. Big bullets going slower making big holes all the way through. Bone breaking capabilities. Elmer Keith
3. Larger frontal areas of bullets transmitting shock and a knockout capability. Many African guides
If one rolls all of these into one cartridge and combine with the incredibly high BC 338 bullets its pretty easy to see why the 338 Win Mag is at the top of the hunters list here in Alaska. Now if (and we have) one can duplicate the rifle 338 Win Mag ballistics from a handgun, one has a very comfortable warm fuzzy feeling when that 1500 pound bear comes to take your deer or elk away from you. Plus you are on one side of a valley or deep cut and a book deer,sheep or goat is on the other side 4-600 yards away you have the capability of putting it on the ground without much effort.
The Alaska Department of fish and Game banned the use of the 7/284 caliber for Bison hunting decades ago for a reason. My friend and many others have taken a lot of moose here when the 7's became popular. Each of those people are now hunting with 338's to 375 Rums for the same reason when asked. Long range shots with knock down authority!
If one tries to compare one school of thought to another, they all have merit. There is a reason why the 338 Lapua Magnum was developed. LONG RANGE AUTHORITY.