Cheers for the replies guys, for you to guage my fuel economy against the Z here's the lowdown -
The S2000 costs just under £50 to fill up and I get about 280 miles out of it in day to day driving with a led foot on an open road. Most roads I drive on to and from work means I'm stuck at about 50mph but I live in the countryside so do go out and about for A road blasts a fair bit too. I then get about 320 miles on a full tank motorway run...probably cos it sits at about 4,500rpm at 75mph