It all depends. I've had an EZ for 170,000 miles and just bought a Quad Race Box. My gut says the smoothest way to haul is stock, and I have hauled something most all of those 170,000 miles. The EZ is pretty flat on the torque curve, not pipey ot peaky, the race box is ... ... ... ... the EZ is hard on the relief valve and probably injectors, the Quad shouldn't be, but is more pipey ... ... ... ... ... ... ... ... . it all depends on your use, undersatand :-{}