I am highly skeptical about power gains from the exhaust alone. I base this on my experience with cat back exhaust systems on several cars I've owned. I have come to the conclusion that I will do exhaust on a vehicle for sound only.
There is a HUGE difference between automotive motors and the scooter motors. On cars, you need a true, tuned exhaust manifold in order to take advantage of exhaust scavenging. Because of this, you will gain VERY little with just cat-back exhaust systems.
On scooters on the other hand, since you are just dealing with a single cylinder, it is MUCH easier to tune it to take advantage of scavenging, and thus really open up a good amount of power.
You can't just do a "cat back" system on our Like since the cat is integrated into the muffler. Not to mention, the exhaust on our Like 200i is like having a Honda Civic SI exhaust on a V8 Camaro. Yes, it will work but it will restrict high rpm flow, thus it will restrict high rpm power.