No doubt about it, 75% meplat will cause more damage and trauma up front, you are on the right path for that. The issue may be feed/function with that larger meplat.
We know for a fact, that .458 caliber +, a 65% meplat of caliber will actually self stabilize itself during terminal penetration, even without any twist rate, or extremely too slow twist rate. We also know for fact that 65% to 70% is optimum for depth of penetration....... below 65% you start to have stability issues, and above 70% depth of penetration starts to diminish because of meplat size..... you trade a little depth for more trauma basically........ but with a good nose profile 75% meplat still gives you all the depth you would need anyway.
I limited the meplat size on the #13 Solids to 67% and we went 68% on the North Forks (John at North Fork just had to be a little different..LOL) This was primarily feed/function in Winchester M70 Control Feed guns. I found if we went to 70% or slightly better, we started having some issues feed/function, by dropping to 67% and 68% meplat feed/function is 100% in M70 Control feed guns. So that is where we are, and the fact that we did not want to drop further for terminal stability.
I am a little lost on 45 degree shoulder part.... but not a concern I don't think?
If you can get your bullet to 75% in .423 caliber and it feed/function, then it will definitely enhance your up front hitting ability and will still give you plenty of good straight line penetration....... In the smaller caliber you might be able to pull it off.... .416 to .423............. Keep us posted, that might be a great development for the smaller calibers...........