Honda 400ex exhaust system
To be honest, I know little about the 400ex (hopefully not for long!) but the Big Gun Evo-R series works magic with my little 07' 250ex! It is insanely loud without the spark arrestor installed, and I am going to change that even if a little power has to be sacrificed. To be honest I'd give the Big Gun a go, I've loved everything they've done so far except their phone service is terrible half the time!