I would agree its much more enjoyable to fireform while you are shooting at vernim then on paper. I shot my personal best 500 yard three shot group with the 270 AM with a fireforming load. A very mild one at that using the 169.5 gr ULD loaded to only a hair over 3000 fps.
This was not the average of the fireforming load but the rifle would seldom shoot much over 1/2 moa at 500 yards. I did not test your rifles at this but I suspect they will be totally usable for some pretty decent range on P. Dogs.
Makes break in go by fsater as well. Especially once you get to the shoot three and clean stage.
The rifle will not kick any more with full tilt loads. In fact it may kick a bit less. With the pressure gets up with the big 169.5 gr ULD the muzzle pressure also increases and the brake will really start to work for you.
Plus the weight of the scope will add some as well.