you would free up some power yes, but it would be nowhere near 20 Hp. I would guess more around 2-5 or so. But I wouldn't worry about it. Some cars disengage the A/C drive pulley at WOT, so this isn't even an issue, because the only time you are going to be using that last 2-5 hp is at WOT.
I am not sure if Honda is the same way though. Someone else can fill in that bit of info.