Regarding the temps. I have to tune for power, fuel economy, and reliability so I was unable to go richer without negatively impacting power and economy. In my case I had to go to a colder plug and adjust advance timing at specific areas in the RPM band. Don't ask, I just have more lattitude in some areas, and more functional limitations in others, than a modeler does.

I don't see much in the way of corrosion with NGK CM-6 plugs but that may because they don't get the opportunity to sit for long periods of time. Then again, the fuel used is tightly controlled (no ethanol, 100 octane no lead racing fuel) and the oil mix is a constant. They get about 10-12 hours off and get airborne again. Under a glass I noted what appeared to be a pitting, or form of melting, with the iridiums I worked with. I'm curious as to what may be evident with the plugs you're working with.