PigDog, I noticed good improvements by fitting 1.72 ratio roller rockers. The car feels torquier and pulls a lot better than before. It revs out to 5,800 easily, however, this may have more to do with the heads. Initially, I was after a cam change but after reading a lot of stuff from the States that the stock cam has a pretty decent grind it made more sense to me to do this as I only wanted something mild.
I couldn't tell you how much power and torque I've picked up because I haven't done a power run yet. I have a book from the States where they dynoed a stock 5.0 with 1.7 rockers and it picked up about 7kw and 20 nm.
I have extractors and a genie 2.5" single system on it but I am a bit reluctant to fit a chip to it because the car is running as smoothly as before. I feel that changing the ratio is better value for money as it will allow it to pick up good acceleration. I realise that I'll lose top speed, but theoritcally it should still see 190 - 200, but then again where can you see that type of speed.