Well. Lou, I would also highly recommend the 45 Colt, especially if you reload. I have an Uberti 1973 with 24.25 inch barrel and an Uberti El Patron with 5.5 inch barrel in .45. I use 11 grains of HS-6, taken as a starting load from the Speer Manual No.12, for the250 grain cast bullet, (Mine are .454 sized) This stays in the 14,000 psi standard pressure range for the .45 Colt. My chronograph shows 5 shot averages of 1200 feet per second at 10 feet, which delivers around 820 foot pounds of energy. By the way, the same load shot from my son's Model 94, 45 Colt with 20 inch barrel averages 1150 FPS. The same load from the El Patron averages 880 FPS. Anyway, the extra 4.25 inch barrel on my Uberti rifle gives me another 50 FPS using this slow burning powder .Bet it would be even better in a 30 inch barrel Accuracy for the 1873 rifles is around 3 inches at 80 yards. My rear sight elevator is set about midway. Have not shot it yet at 100 yards or more because of heavy timber where I was last shooting.
Also I experience almost no blowback in the rifle with this loading and it has proven safe for me.
Of course, we all must adhere to only using standard pressure loads from the reloading manuals when loading the weaker 1973 actions.
I do not know how this might compare with a .357, but you have the additional greater caliber of the .45 and the greater bullet weight in the old warhorse's favor. I do not have experience with the 44.40, but as others have said, it is both traditional and well proven. I would take a long look at it, particularly if you have a .44.40 six shooter. so there is my 2 cents. Best Regards,