One thing as you mostly know, you are limited to 45 LC in mounted ( unless something has changed since I last competed in Mounted in 01 )
( also retired from active Mounted Cav. Reenacting ) I still ride and do Cracker Cowboy and Creek War events one or twice a year.
I used Rugers 7 1/2 " SS ( same guns I used for CAS )
I believe then and now the 5 1/2" is handier on horseback, but the 7 1/2" were my reach out a get-um balloon buster.
If 45 LC suits you as a main match round ( it's my favorite ) your good to go for both Mounted and CAS.
I think the Taurus is offered Nickel not sure about SS.
If you do some looking you will find some 45 LC Rugers at attractive prices under the cost of new Taurus.
As you said SS is easy to clean with the BP blanks and will serve you well.
If you clean your guns after use (rather than wait days on end ) that should not detour you from the Blue and Case color you like.
Now days, I'm more into style, always was into authenticity, so the Rugers are gone in favor of Opentops.
hope that helps