Well now, balance and especially aesthectics are both highly subjective, so ya gotta go with what you like. I have had and still have some 7 1/2" guns, both SAA and conversions, but I shoot the shorter barreled conversions more. Yes, because quicker to handle for CAS. In fact, my smokeless main match guns now are 4 3/4" '51 conversions. But I do love the look of the 5 1/2" guns. But then, my hands are small and so I like Navy grips and trade army grips for Navy. IMO (again, subjective), shorter barrels with Army grips don't look quite so good. As for '60's, I like the look of the Richards more than the Richards-Masons due to the barrel shape. You seem to prefer a .45 for the '60, so this wouldn't affect you, but both the Richards and R-M '60's from Uberti that are in .38 are actually '51 frames and cylinders with Army grips and barrel. I took advantage of that to change a '60 Richards to a '61 Richards by simply changing to Navy grip. I also changed a .44 Richards grip to Navy, which isn't authentic but I don't care and the originals could have been changed as well if someone preferred the Navy. I know longer barrels were much more common, but that's okay. I do like the aesthetics of the 5.5" Richards. And yeah, if you get a Richards vs a R-M '60 then you will HAVE to make new leather since the barrel probably won't fit in anything else you have. But hey, no problem for a leather worker! 
Thank you for the information. Yeah, I would def want to get them in 45 because I have four 1851 RM Conversions all in .38.
Those pics your posted are very beautiful revolvers. Like the white grips on yours also.
I will have to study more on the differences between the Richards and Richards-Mason 1860s.