As evidenced by the cartridge choices the Super Redhawk follows the connotations of it's name and can certainly call itself the stronger gun. Where the 'better' statement comes from for me is the traditional two-spring approach to the mechanism. One spring for the trigger return, one for the hammer. With the two spring approach the trigger is both better out of the box, and can be improved much more simply.
Now the Redhawk has an ingenious system using a single main spring which I feel is FAR more clever, but in reality clever does not trump the trigger feel at the end of the day.
That being said I see a custom Redhawk in the Bowen site, in my opinion equal parts because of the clever mechanism and the beautiful traditional lines of the pistol.
I wonder if the SRH frame is in fact practically stronger. As you say, the RH has been chambered for some very heavy loads by Bowen. I understand that for the SRH in 454, the additional functional strength is a result of the stronger steel used for the cylinder (which also allowed ruger to keep it as a 6 shot instead of a 5).
It is my understanding that the SRH was designed, at least in part, in response to a frame cracking problems with the RH. It turned out, the problem was due to a particular bonding agent applied to the threading where the barrel screws into the frame. They fixed the problem and opted not to discontinue the RH (no doubt in part because there is a market for the more traditional design). Other than the original issue that was corrected, I have yet to read a case where someone has shot loose a RH (i certainly have not done an exhaustive search, but i have had my eye on various gun mags over the last few decades).
Also, I've read that some prefer / think the RH SA trigger is lighter out of the box, but the SRH is easier to tune. For me, having owned a RH and a GP100 (same internals as the SRH) can't say i noticed a huge difference in the SA triggers (granted i never did a side by side comparison).
Anyway, not trying to say the RH is as good or better than the SRH, but to me, the SRH seems to be an incremental improvement, not and evolutionary one. I would not pass on a RH, thinking the SRH was vastly superior.