I am trying to deiced which between a RS-4 or a RS-4D exhaust to for my 2011 CRF250. According to the Yoshimura website the RS-4D should make more power in the bottom end and the RS-4 should make more up top, but I must wonder if it is a bit of marketing hype. Has anyone tried a RS-4D yet? I can't find any reviews on the RS-4D to make a comparison. I prefer the look of the RS-4 but if the RS-4D actually makes noticeably more bottom end power then I will by it. any help will be greatly appreciated.