I didn't realize that there are apparently several varieties of Plymouth Rock , including a Buff variant. Would the other variants have the same temperament as the Barred ?
Well....

Each chicken really is an individual, but I've found that they do share similar temperaments/personality/mannerisms. I will say that I've only had Barred and White Plymouth Rocks, so can't tell you about the other colors.
My Barred are bolder/have a stronger personality than the White, but someone else that has them, may see just the opposite.

I have hatchery White and Barred and then a few "breeder" Barred as well. There is a difference between all 3 that's for sure. The White are a bit more shy and flighty, while the Barred are calm, confident/self-assured. I hesitate to use the word bold because that sounds negative, but they do have a boldness to them, but not in a mean way.
The breeder BR are still young, but have that same self assured calm manner that I like.
There is a little difference in looks between the varieties as well. Overall, I like the Rocks, but Orpingtons are a favorite too
btw - Orpingtons come in blue, black, splash, lavender, white, jubilee and probably a few other colors!
You can see the differences in mine here. First one is hatchery BR mature older hen, second is hatchery WR hen and the third is "breeder" BR pullet with cockerel.