BRs have a bigger shock, which holds more oil, and is apparently better quality oil too.
I have BRs with the standard spring rate, and I think they're pretty good. Set to full soft, they're way too soft. I run mine about 5-10 clicks from hard.
BRs are supposed to 'be for track' because the larger oil volume means the oil doesn't heat up as quick (apparently), and they can take more of a beating.
I know Leon ordered his with a softer spring rate, about 1-2kg softer front and rear, and he's really happy with them.