Well, I think you can look at the Military for ton's of evidence, experiance and testing. Thus their current configurations.
Successfull offhand shooting has ALOT to do with human body ergonomics/muscle control. You must consider the human factor, the gun itself secured by vises will or should shoot one hole. (all things considered and made same, including ammo)
I shoot alot of off hand during Rendezvous season and pistol grips are not part of that. The successull shooter is one that understands his;
physical condition,( you need to excercise)
muscle control and diet, (you have 15 seconds during a hold, before the muscles need to recover energy)
Breathing and Heartbeat, (again physical)
Drift and trigger control, (you are going to move while holding)
Stance and "Natural Point of Aim",,,
There's a bunch of stuff,,

Anyways, given an option of stock configuration, the thumb-hole and a wide/large forearm lends itself to better off hand shooting. Simply because of better fit to the human body, guy's don't go out an get custom fitted stocks just because they look cool.
