My car has a similar set up to yours Stephen, G56 exhaust and filter, 569 cams with roller rockers. I must admit the 569 cams and rockers were certainly not essential but, to my mind at least, they do make for a smoother power delivery and a bit more "go" through the rev range if you want it. The economy hasn't been reduced by much if any, if you drive it modestly. Not sure about the Emerald ECU that you are using but the S&S one does have a rev limiter function, usually set for a soft cut at 5500rpm as standard I think but that can be reset to 5700 soft cut and 5800 hard cut to get the full safe limits.
