I've tried 9901 and 2045 on a Killer. Many drivers likes the performance from the 2045. I found the 9901 gave the engine more power. With the 2045 the engine was quiet lame, but perhaps easier to control for some drivers.

At a race last month I was pitman for a RB Fire. The engine ran ok (under 2 liters of fuel). When we changed to a Novarossi C6TGC plug the engine ran PERFECT. HUUUGE different in performance between RB#6 and Nova plugs. Perhaps the RB plug was a "monday" plug (it was not the plug that was used during break-in).