Haxaw, I love the 50, it's louder than stock, but not a lot. On these cold Chicago mornings when I have to warm my truck up, I have no worries about waking up the neighbors. It has a nice throaty tone to it when you get on it too. I haven't noticed any MPG gains, but it does feel a little stronger HP wise. The K&N helps too. This was my first mod, and there was a slightly noticeable HP and MPG gain with that alone. The subsequent mods have negated the MPG gain, and some say it may be due to the extremely cold weather here. Right now, my city mileage is about 10 MPG. As far as the KKM or FIPK, it's a toss up. Do a search on the site and see what members who have them think about them. Some have mentioned the fact that the open filter will tend to suck in hot air from the engine compartment, and are trying to form some heat shields to create a "cold air box" around the filter. Hope I could shed some light on these few things for you. If you have any other questions, feel free to ask.