the sito plus and the sip road are completely different pipes.
the sito plus is a copy of the t5 pipe with what sounds like no sound deadening matirial, a hate them due to the noise they make but they let the t5 rev out better.
the sip road is a standard p2 pipe with cones added to make it into a clubman, its so quite that it makes riding every day a joy (unless you wear a tracksuit and like revving the crap out of your scooter in the street for no reason, in which case you will hate it)
i have used both and the difference that going from a sito plus to a sip road was a real surprise, with a power band and plenty of grunt.
no disrespect to diablo or any other tuner but you tell the tuner what you want not do what the tuner says, thats how so many people end up disappointed with a race engine that will not pull their mrs and pav trailer on their touring holiday.
train driver has a rz right hander and a sito plus so i say try both, get carb settings for both then just swap for the one you want to use.
the rz has quite a nice deep tone on a vespa so he could be happy with it