T5's are great trail duner pipes and liked them way better over Fatties, I replaced them with CPI's and get way better response from the motor. Now have dune ported cylinders from Wildcard Racing to match those CPI's and will rip even better. For that 4mill I would suggest CPI, Shearers, FTZ but your builder has to port your cylinders to match any type of pipe. I need spark arresters as well and have plans to modify a set. I will purchase a set of silencer end caps from CPI & a set of USFS approved Cobra Sparkies, will cut and weld together. This way I can simply unscrew my end cap and screw on the modified end cap with spark arrester. If you're sticking to T5's you can use the Fatty stingers and silencers with them.