The difference between the RS and RR models as dlai said is the muffler. In the RS there is one, in the RR there isn't. There is also no resonator in the RR, but there is in the RS. Im running no cat in my exhaust, and have had flanges put on the resonator so it can be removed whenever I like. At the moment it's out, replaced by a straight pipe.

With no cat and no resonator the exhaust is loud, but not stupid. Take out the muffler and then it'll be crazy loud. Also bear in mind if you run a decat system you're going to have issues with CELs. Only way to guarrantee you won't get a CEL with a decat system is to run a kpro. That's what ive got.

Unless you've got a built engine, I would avoid a 70rr. It'll sound nuts but you're going to lose power because there will be no back pressure in the exhaust, which a cat, resonator and muffler usually provide. If you pm me a mobile number I can mms a sound clip to you.