I have a 5.5" Redhawk in 45 Colt. It is an excellent shooter. You can load them up to some substantial pressures if you so desire, even above the Blackhawk. I traded a Beretta 96D for it at a gunshow. As I recall, the dealer made a half joking remark about finally getting that one off the table, but that was about 10 years ago. I think I got the better deal.
The 45 Colt offers some definate advantages if you are a serious handloader, but not so much over the more readily available 44 Mag if you are not. That is probably one of the reasons for its demise. I also think a lot of folks preferred the Blackhawk for a hunting handgun, there being no specific need for a double action in most field situations. With heavy loads, there is some advantage to the BH grip in that you can allow it to roll up with the recoil to dissipate some of the energy instead of it slamming back into your hand like the RH grip. But some folks just don't like a SA grip nor do they shoot it well, thus the RH's niche.