Hi Colin,
I'm no engine guru lol, I got mine remmapped by http://www.andyforrestperformance.co.uk/index2.html. It's worth a read and should answer some of your questions mate. I went for the Ecutek ..and i'm lead to believe the OE ecu on the later models '99-'00 responds well to this.
I'm sure someone more knowledgable will be along shortly to give you some useful advice
HTH's
Framk