The largest gun I feel comfortable carrying AIWB is my Glock 27 with the grip enhancer. I carry all the time hiking and working outdoors. If I was going to be sitting for hours without moving it may get uncomfortable. With a proper holster and belt it is quite secure. My J frame is slightly more concealable, but comfort is about the same.
It is not for everyone.I guess that is why we all have a box (or 2) full of holsters.
Jfootin; That is where we differ, I on the other hand try to obtain a firing grip before I draw, but, that is my training. I also keep my finger off the trigger until the gun is up, that is training as well.
My rifle and pistol are tools, I am the weapon.