I never used the RAD valve,but I hear it moves the power to the top end and its not really making more power,just moving it.But most of us KX500 riders have a more responsive,little more power by using the V-Fource.So like I say I can suggest a V-Fource as money well spent,as far as a pipe I run a PC.But I would say the Gnarly for real tight tracks and the Fatty for every thing else,or if just one pipe go with the Fatty.