I just changed out my Denso plugs to Bosch Platinum +4 plugs after 30,000 miles on the Denso's. I almmost feel like I can sense a power increase after changing the plugs. Everybody at the Toyota dealer used to tell me that "you must use NGK plugs man nothing else works" and blah blah blah but the Bosch lugs seem to work great. The engine runs very smooth, develops good power, and I've seen no ill effects from the non-NGK plugs at all. Do people say that you must use NGK simply because that's what the Toyota manual says or does anyone have quantative data to prove it? I hate it when people speak from the wrong orifice!