You mean the MXP and MXC? MXC is forged magnesium and the MXP is cast magnesium. Personally I never saw much of a difference at all between the two wheels when the setup is correct. The MXC’s strong point are the long run of a race on a sticky tire, but if you have your tire pressures figured out and chassis close to 95% you can still win a big race on MXP’s in a long run too. Either wheel is proven capable of winning.