Modern Vespa

assuming using the same contra spring, what difference do the different brands make for performance and how? eg, malossi vs oem etc

or is it bs?

I believe the slot in the torque driver is prefered to be straight narrow angle for competition. Road or stock ones are more curved shaped. My scooter doesn't like changing down gears on slight slopes at lower rpm as I don't have enough grunt to overcome the pin friction. (Coast down a slight incline at 40-45 mph and the tramsmission shifts to its highest gear. Then on the following uphill grade at say 4500-ish RPM I gon't have enough grunt to make the CVT change)

Maybe a straight slot unit would solve that but I don't think anyone makes one (Honda)

On smaller scooters the straight slots seem popular as they don't have much HP to play with.

Can't comment on various manufacturers esp. Malossi as they will not divulge slot angle. You have to buy one first and measure it yourself.

Of course the slots only come into play at road speeds below the CVT max engagement speed.

interesting ... 🤔

From a site trying to sell them. I haven't found much else and not one with straight grooves for mine.

Oh, and one site did say stock angle is 41° and their angle is 37°

All the fussing around you can do with a variator system has an effect on the relationship between the rpm of the engine and the rpm of the rear wheel, but the engine can't rev any higher than its ignition system allows, and the aftermarket electronic replacements for the CDI system that permit higher revs expose your engine to possible failure. You can style a drive system that requires a higher engine rpm at a given road speed, giving snappy performance, but that costs you top speed. If it was easy to make the scooter accelerate faster without a tradeoff, Vespa would do it.

Sadly no, they build for the mass market who just want to go from A to B in an Italian village.
I've put different weights in mine and did not lose and max. speed. But I rarely used max speed.

100%

Stock is the most reliable though?

yes.

No.

depends on which part you are talking about