The manual for my 00 GS-r suggested NGK and Denso. I just had the Denso plugs put in w/ magnacor 8.5 mm plug wires and I noticed an increase in fuel efficiency and it may be totally unrelated, but it seems to start easier regardless of temp.

If I understand it correctly the purpose of using different materials in plugs is to affect the temp of the spark itself. The Denso iridiums had a much higher spark temp.