Is there any performance advantage to a Iridium plug?

.... over just a stock 4548? (other than it out lasting the bike)?

Nope. Just longevity.

If you allow the stock plugs to degrade to the point that the gap begins to open up, then you will notice a difference when you throw a set of iridiums in . . . but it would be the same difference as putting fresh stockers in.

That said, I run iridiums because I don't have to drag out the wrenches as often.

Yeah, probably worth the few extra bucks! Thanks.