Simon - not sure what pistons you are using, but there is a useful table on the K Black piston site at
http://www.kb-silvolite.com/speclear.htm#CHART
It gives ring gap recommendations for a variety of applications, but bear in mind they are for hyper-eutectic pistons, not forged ones.
Tom - out of interest, would the type of piston used (forged, hyper, plain cast) affect the ring gap requirement, or is this independant of piston expansion characteristics?
BTW - a great pleasure to meet you in London Oh.