get rid of thoses things as fast as you can. i suffered a blown head gasket cause of that. how much did you get your plugs for cause for about the same price you might have been able to get oem plugs. ive tried every kind off performance and gas saving plug there is. none were better than oem. not to mention im boosted. my car calls for ngk copper and thats what i use. no upgrade to platinum or ix keep oem. dont do the same mistake i did. $60 spark plugs cost me $900.i'm running NGK IX's and i think i'm noticing a Little Misfire at idle. they are Iridium plugs. so i'd avoid them. i've checked the gap about three times since installing them (which is a pain lol) and its been Perfect everytime.
You won't notice any difference in performance or mileage.You won't see a fuel efficiency increase, unless they were really bad. I wouldn't get my hopes up.