I'm getting ready to change my spark plugs on a 17 RGS, which already has a Stage II torque cam and ventilator air cleaner. HD offers stock plugs for about $5 bucks each and Screamin Eagle Performance plugs for a few dollars more. Does anyone have an opinion on the Screamin Eagle plugs? They say they are designed to go with Stage upgrades. I'm really not concerned about the few bucks more that they cost. I just want to know if they actually make a positive difference.