From everything I've read over the years, 5100 is not the same as RR. They're definitely, and obviously, both red VA, but the crops used to make RR are carefully selected, and to my eye are of a higher grade than what's generally used in 5100. Anecdotal evidence here: more stems in the bulk than in the tin, for example.
Some people find them similar, others different. I imagine (but don't know) that the constituents of the 5100 quietly change more often than RR changes -- and in the case of RR, those changes are declared by a different vintage on the tin.
I like 5100 very much, and have a quantity cellared. But RR is a step up, generally. It may have something to do with how the crops are aged prior to tinning, or the choice and grade of leaf used, or some other combination of factors. 5100 is sweeter and maybe a bit one-dimensional (which can be good, sometimes), while RR is rounder and more supple.
Try them yourself and see what your palette says. That's all that matters at the end of the day.