I know this exhaust
Sorry, but this makes no sense in your case.
You only have a DR130 which is no high reving race barrel.
You did not do anything else on this engine - you just clamped the barrel on the standard engine and that was it. You only have a small carburetor, no racing crankshaft, no adapted gear ratio etc.
Before you start thinking of such exhausts, I would reccomend to get the principle mechanism of a rotating-valve 2-Stroke engines back in mind.
As 2-Stroke engines are designed in a particular way, you cannot just fit every type of exhaust.
This Simonini will reduce your driving fun.
OK, maybe you might get some extra revs in the upper rev segment (which makes the engine faster on ideal conditions), but you will loose torque in the lower revs, also on the hill, with headwinds or when your take a second person with you.
Your entry question was to gain some extra power, but the Simonini will not do this.
Also...You will have to remove such exhaust everytime when you want to change gearbox oil (which you should reglary do once a year or every 5000 km).
Also...it doesn't sound good...sounds tinny....it is just a cheap thin italian pressed metal...