Epoc, Send Xpower a PM, he can help out with some info on gains. He backs his shit up with proof.
Also, be careful with your approach as ultimately it is your money and your car, rid any biasm that yoo may have to a particular product. Do thorough research on any product that you have an interest in. I'm sure that you are aware the internet is full of BS and Fanboys. Besides i'm sure you have worked hard to earn your cash, why not do some "homework" before you part with it?
for example, go and have a look over at E90post for some insight into how people just believe any shit spewed to them by fellow posters and take sides in the "JB3 vs procede" battle without even knowing the difference in approach, tuning, benefits etc etc. Just a bunch of sheep imo.