I have large hands, and the straight grip on my .450 Marlin allows for more unimpeded movement when levering my rifle and recovering from recoil. I have a large nose, also, and sometimes, I have to be careful about my positioning, lest I get hit in the snoz! I like both, but for a heavy-recoiling rifle, I like the strraight grip. I'm not sure of the scientific reasons, though. Many heavy double guns used in Africa have psitol grips. I guess to each his own.
PS I think that the combs and stocks on pistol grip rifles are generally better fr scope use. I use peep or Express Sights on both of the above mentioned rifles