Jeff,
Beyond a certain point, you are correct, you are gaining nothing but flatter trajectory. Now, you can get the velocity up to the point where you will see more action on target, but your shoulder will bear the punishment.
Let's do a little testing here. My .45-70 black powder loads feature a Lyman Govt bullet that drops from the mold at about 522gr at 30-1 lead to tin. A soft bullet, to be sure, so we don't want to push it so fast that it comes apart. Fortunately, my Shiloh shoots it at just over 1100fps.
"Why! That's a wimpy load!" you might say. However, with wet newspaper tightly packed together, it penetrated in a straight line 65 inches and buried itself to the base in the 2x8 that backed the stack. Pretty impressive for a wimpy load.
Get your bullet weight up over 400gr and get your velocity up over 1200fps and, if you have one of Veral's designs, there is nothing you cannot take that walks this earth.
Now Veral can make you a mold that throws a bullet that will really put the smack down on them and his molds generally will work with tougher alloys, like wheelweights. You can push them a lot harder.