The heat range does have an effect. I was running bp5hs without problems with a top speed of 62-63kph and switched to a b7hs and lost some top speed but gained in bottom end. So i bought another set of plugs. Brp6hs and i have a top speed of 65kph and bottom end is good.
Bu i also have a bunch of mods. Home made ram air, i extended the exhaust to the back of the bike with two expansion chambers and a muffler, i raised the pin in the carb to give it more gas.