I would wager that all intake systems will be roughly (read: +/- 1 or maybe 2 HP) equal in power gains. Whether you'll feel a difference between intake Z and intake X is highly unlikely. Go with whatever has the biggest filter.
I went with performancefords.com cause the guys are 'tour owners, work hard to get new products out for our cars, and the piece looks like it will be great quality. If you're interested, I'll be giving my thoughts w/in a day or two (when it comes in).
