I have Denso iridium fine wires in my 73 850 right now. I had been having some fouling problems - combination of too rich and I think a bit of oil from the guides. These plugs haven't changed my mixture or replaced my guides - that's my job - but they've kept the bike running and it hasn't fouled a plug since.
Bottom line - I went out and put the same plugs in all 5 of my bikes (or NGK iridium fine wires, in the case of of my wife's Bonnie - Denso didn't seem to make a plug for that bike). 'Course, I'm a bit of a nut about this stuff...
FWIW.