so guys, how many miles or time can you really get out've an iridium plug in a 929. i know that spark plug life is dependent on what you put it through, fuel ratios, temp, etc, but they're like 15 bucks each and i wanta get all the good out've them. thanks for the opinions. also, what brand should i go back with? it's got denso iridiums in it, but , what brand, and is iridium really perform better?