I, too, think the 50 will be king of the hill for the majority for a long time. It works, works well, and has a tremendous # of sabots/bullets,etc for it as well as a few states mandating it.
Regardless, IMO, the 45 has everything else going for it. Less recoil, adequate killing power, at least equal accuracy, enough very good bullets - how many do you need!?, and the ability to shoot saboted 40 and 357 cal bullets and bore sized 45 cal bullets. You just don't get better bullets than the Parkers and they shoot extremely accurately sabotless w/o any of the sabot drawbacks. So the 45 will do anything the 50 will do with up thru 300g bullets and can shoot the aerodynamically superior 40 and 357 cal bullets. It just doesn't matter if one cal has 50 different bullets for it if the other(45) has enough great choices for an excellent load. If a 250, or 275 45 cal Parker BE, or a 250,275,or 300 Parker HC 45(also bore sized) - also sold as Remington and T-shocks respectively - all 5 bullets bore sized and great bullets, and 200SST, various DCs that will shoot well to at least 2300'/sec, 175 and 195 Barnes, and 235 Hawks, if all these aren't enough, and all are great bullets, then something is wrong. It just takes 1 good load. My problem is that of the 8 of these I've shot, all are so good that I have problems deciding which to use.
I know of no one who has tried a 45 going back to a 50. All 3 of my ML-2s are converted. The only 50 cal I shoot is the one I maintain/store for a fellow hunter who doesn't know how to clean nor care for his ML-2. I just give it to him loaded and slightly fouled at beginning of season and take care of it after the season. Just my thoughts on 45 vs 50.