I have the same desire, my truck has shorty's on it and me personally I don't like them, and I agree with dartboy that there will be issues with clearance's how ever I did look at that link and it doesn't actually say what truck size its for it just says pickup. Based on how I see it if u have clearing issues the safest bet would be to use a torch to heat up the tube and try to bend them that way to try and keep them relatively clean. That is how I would do it but I'm thinking of taking a different rout on the exhaust I have not seem before. As for the power difference all long tubes do add some torque gain and yes the size does have a effect, but for a start point you cant really go wrong with that size and you can always change the collector later to something bigger if you wish.