I've read dyno tests before that indicate they are only worth 5-10 HP at the most on stock heads. However, if you ever install aftermarket heads, you are going to want RR for them, and they are
usually transplantable, plus, you will see more of a gain with them on a set of heads that can actually take advantage of the extra lift (where the stock heads really don't).
So really, its up to you, just do your homework and make sure you are getting a set of RR that you won’t have to get rid of when you put new heads/cam on your engine.