don't forget the change in front swaybar mounting point on the strut... maybe the smaller bar is more effective because of that. I've never measured it, but I would be surprised if Honda changed the front rollbar effectiveness that much between the 06 and the 12.... but maybe they did.
Anyway, I highly doubt the bigger rear bar will make the car dangerous at normal road speeds (less than 65 mph). At higher than legal speeds though, you will probably have to be more careful.
Chris
Why would a larger rear sway bar be dangerous at high highway speeds?