With BP and BP sub MLs, the 45 gives only a marginal advantage in velocity that one may argue is hardly meaningful. Typically, you are using the same .40cal bullets as the 50 can shoot to do this. Now is someone would come out with a jacketed bullet that looked like the 195gr .357 DC, I'd be tempted to add a 45 to the stable. Right now there are not high BC jacketed .357 bullets available that do the caliber justice.

In the smokeless ML world (ie Savage) the .45 is gaining popularity because the .50 version of those won't shoot the .40cal bullets as the violence of smokeless ignition is too much for the thick sabots. The velocity difference is also more meaningful.

I shot the 200SW for years out of a .50, I guess I could have tweaked it a little in a .45 to gain a bit of velocity. However I can shoot the .458 325gr FTX in my 50 but not in a 45, and get the same trajectory with double the energy. Just a little more punishment on the shoulder.