I've had a SRH 480 for about 1 1/2 years now, with several thousand rounds through it. The frame is very strong, I know a few foolish soles have had their 480's re-chambered to 475 linebaugh, and yet they haven't blow them up yet. The SRH does lock up in the front of the cylinder as well as the rear. Mine was never bank vault tight, but scoped off the bench it'll print 1" @ 50 yds with worked up loads. I've shot numerous different styles of cast bullets through mine, and all do quite well.
The only Raging Bull I've ever handled was a 454, and to me it was bulky and I didn't like having two releases on the cylinder. The only Mag research guns I've seen are the 45-70 monstrosities.
The best bet would be if you could find some owners of the various guns and test fire them. A buddy had a 480 SRH, and I wanted one as soon as I shot it. For some reason I'm able to shoot the SRH much better then a single action. I have absolutely no complaints about the SRH.
Here is a link to my cast bullet loads:
http://www.serveroptions.com/ubb/ultimatebb.php?ubb=get_topic;f=25;t=000222