It is easy to see what you and Fred love about these WRs, they are great-looking birds! Is there a huge difference, or not much at all, between White Rocks and Barred Rocks? Can't have white birds here.
The Rocks are all bred to the same standard as each are intended to be varieties of the one same breed. Whether Barred, White, Partridge, Buff, etc.
But the fact is that while the breed is determined not by pedigree but by rules of color, shape, etc, the making of these different varieties produced some differences in personality, I believe. I've never owned some of the varieties. Cannot speak to their personality.
The White Rocks, at the good ones I've had, simply have the best personality, for a chicken, that I've ever had. None of our hatchery based Barred Rocks ever exhibited quite the same all around "goodness". The heritage line I have now absolutely does! So? I dunno. All I can tell you is that the WR is just different, in my experience.