Not trying to be a jerk or anything, but I disagree man.
You can put any sprockets you want on there for your application. Obviously some gearing combos will just SUCK because you will be geared too low or too high. But, why on earth would anyone leave it geared horribly wrong? It isn't like he is going to destroy his bike by trying different combos. Different people will like different gearing. I think it is pretty obvious that something like 13 in the front and 50 in the back won't work too well .. LOL.
There is no "max" number of sprocket teeth you can change without "losing" hp. It all depends on your application and preference.