One other main differance on MPi Abarth's and Schumi's which show they were stand alone models rather than have the option list ticked is they have a shorter final drive on the gearbox to make up for having the bigger wheels so acceleration remains the same.
Spi models with Abarth extras didn't have the shorter drive gearbox.
This gearbox translates to roughly running 500pm higher at 80mph in 5th gear than running a normal box and the same wheel configuration.
MPi models also get red stiching on the steering wheel, not sure about Spi models think its just standard black like all other Sei models.
As correctly pointed out the alloy pedal covers, handbrake handle and gearstick surround were standard on Schumi models but optional on ALL models. Our Mpi Sei Abarth has the handbrake handle and gearstick surround, though we use Panda 100HP optional pedal covers.
There was a fair few other optional extras like carbon look dash panel which again I think Schumi models got as standard, sill covers, headlamp pretectors, and a very nice three spoke air-bag steering wheel IIRC.