Don't know about the E3's personally but just read this on another corvette Forum:
"Last Easter Sunday I was driving my wonderful 1998 C5 and it started to run really rough, wouldn't idle, smelled like sulfur, and missed like crazy. I was freaking out(old 70's term). I did make it to my mechanic, left the car, and waited till Monday. Turns out it was a bad plug in the #2 hole. I can't believe that a bad plug made the engine run so freaking bad. I've had E3's in the car since 08-08 and it ran great till now. I checked on line and found other stories like mine involving that plug. Needless to say, they're coming out now. By the way, they're all a nice caramel color. My question is, what is a good plug for a Vette engine with 151,000 plus miles on it. The car still runs great and I wanna keep it that way."
I don't know the person that posted the thread but it sounds like he has done some checking on them?
I gonna try the NGK iridiums.