I have ridden Brasstown Bald (even time trialed up in the early 90s as part of the Athens Twighlight Crit weekend). Of all the southeastern climbs I have done, including Mt Mitchell, Brasstown is definitely the toughest. Overall, I think the grade is around 12%, but there is a 20% section that many riders zig zag through. Some off the best sections near the top are on a closed road though, which I think you can only ride during official events like the Brasstown Baldbuster.