I've never ran the copper ones, up till now mine have usually called for the more pricey 100k mile ones. except for my expedition, I pulled copper ones out of it and replaced them (only saw a misfire caused by that at around 125k, can't remember if it was iridium tipped ones or what, I'd have to check my orders) about how long do the copper ones go between changes?
It was platinum they called for and I upgraded to the platinum on the expedition when the copper ones I went back with only lasted 15k miles. since these are so easy to get at I will go with your recommendation for copper. and make a note of the replacement interval.