Which header is better?

I'm looking for a header for my 1991 KZ1000P. Is there any information somewhere showing the horsepower gains over stock with each of the aftermarket headers on the market? I'm going to rejet the carbs and get rid of the airbox. And that brings up another question. Do you have to remove the carbs to get the airbox out? It looks that way to me.

if you find one that fits let me know what brand it is:)