You won't feel any gains from new spark plugs unless yours are just incredibly shitty or really really really really worn out. For a Gen 5, you won't feel any difference. The only thing I got was that the car starts easier, especially on cold starts.
I use Iridium IX aswell, fantastic plugs. You won't gain anthing by using them, apart from less spent time etc in removing your intake plenum and replacing the rears if you have a V6. These last around 100k. If you have an I4, you can use them still, but maybe not worth it, as changing plugs on it is a sinch.