I run the iridium plugs in everything from stock cars to Rods engine on all the topspeed runs and I like them and have never had a problem with them,
I have not tested them back to back with other makes so I cant tell you the diff only I like them , If I get chance to try a diff type of plug on the dyno I will try and see if any make any diff.
Some people hate the Iridium plugs as they blame them for breaking engines but I have not found this to be true and I have run these plugs hard .

Mark