ChevyFazer
Redneck MacGyver
It all depends on what you want, it sounds like you want more tq which stock would be best. But there are plenty of advantages of having a aftermarket exhaust, less weight, less heat, more noise (a disadvantage to some) better looks and if it is properly tuned you will get power gains on the top end. Add a healthy air box mod with after market filter and de-cat pipe if the exhaust didn't come with it and your talking about ~10hp extra to the wheel which is quite a jump on something that only weights ~450lb. Plus on 90% of vehicles a performance exhaust can also increase fuel economy by allowing the engine to run more efficiently. It would be extremely hard to see a increase on a bike though because once you have a exhaust it's hard to not make it wail sending intoxicating sound waves up and down your spine!!!
That is what it's all about the power to weight ratio, yeah exhaust alone might only get you 5hp but that is still quite a bit for a bike. Now if we were talking about a car, yes that gain would be trivial. But from one of your other threads it seems you are looking for more tq not hp. And really there is only 1 thing that will significantly improve the tq and that is a sprocket change.
That is what it's all about the power to weight ratio, yeah exhaust alone might only get you 5hp but that is still quite a bit for a bike. Now if we were talking about a car, yes that gain would be trivial. But from one of your other threads it seems you are looking for more tq not hp. And really there is only 1 thing that will significantly improve the tq and that is a sprocket change.