Brock's Alien Head exhausts make more power over the Predator line-up. The Predators look better though IMO. There's maybe a 1-2HP difference on a generous dyno but if you're looking to split hairs there's a reason the Alien Head is the preferred can for the drag (where splitting hairs > aesthetics). In terms of sprocket changing it's all subjective to what your application is. I've been told a +2R is the go-to for the Gen4's...