The TopPerformances Nardo, Giannelli Nardo and Giannelli Shot are (almost) the same exhaust. The TP Nardo was developed for the TP Due Plus cylinder, then Giannelli took the Nardo and called it the Giannelli Nardo, and some years later they called it the Giannelli Shot. So you won't notice any difference in performence between these exhausts.
I think the MHR Rep + Shot/Nardo is a very nice combination.