That is a fantastic pair with top notch provenance. I like the 4.5" barrels too.

I often wondered what the rationale was on the RM's when people had them built in non-standard barrel lengths. One theory for owners of 4.75", 5.5" and 7.5" RM's is that their owners were familiar with those lengths from Colt SAA's and other popular models, and figured there was some combination of ballistics and handiness with each of those lengths that appealed to them.

Or maybe they just wanted something different ? Production figures show that the most common 3.5", 4", 5", 6", 6.5" and 8.5" or later 8 3/8" guns met the needs of the majority of buyers.