It has been about 20 years since I owned one WFO but wasn't there something different about the silver body Super BN's? I thought it was their "High Performance" series or something like that.
I also remember the Yamaha ones were a little different that all the other Super BN's too.
WFo knows his stuff. But back in the day we would only use the Silver body Super BN 44's on the Kawasaki 650's with the Ocean Pro Vortex FA's. Like I said though I don't remember why they were "special" at the time.