How much more power do you get when you change the exhaust on a 1991 cbr 600?

The truth of the matter is that it is a common misconception that putting on aftermarket exhaust is going to give you more power, well it will at the peak of your powerband, but that is it, but in fact you will lose more average throughout your power band, meaning that it is nly a good thing to do if you are constantly near redline, ie: racing on a track. lets say your cbr puts out 100HP@14K RPM's, well you might go up to 102HP at that same RPM, but lose 5-10 hp throughout the rest of your entire powerband. Aftermarket exhaust companies know this, but only give you peak HP figures to make sales. If you don't believe me look at any before and after dyno. To help a bit, my friend and I have the same exact bikes being 06 zx6r's. His best 1/4 mile time is 11.8 seconds over multiple runs the same day, I was pulling 11.1 seconds on mine, given it was a very hot day. The difference? mine is bone stock, his has an aftermarket exhaust, air filter and power commander, and we run the same gearing and same tires. but on the flip side his bike's top speed is almost 1mph higher than mine, but I'll be long gone before he hit's it. Simple answer is; aftermarket = less power everywhere except on the last 1 or 2 k rpms which means slower off the line and low rpm to high rpm acceleration, and I don't know of too many tracks that you're going to constantly be in your peak rpm anyways,they also weigh a bit less, but not nearly enough to make up for the lost low and midrange hp. Bike Manufactures have a hell of a lot more money in R&D than exhaust companies do, so they know what their doing. So if you're on the street, save your money and make your bike more personable and custom vs. doing what every other idiot thinks is the way to go.