I recently reached 75,000 miles on my FX35 and decided to have the plugs changed.The Infiniti service man told me the plugs were good for 150,000 miles and I could wait.I opted to change them anyway and was surprised to see the condition of the old plugs.All were gapped at least 10 degrees to wide and one had a metal burr on the tip.I chose to install a hotter plug than the standard one because I do most of my driving in the city and the carbon build up was ridiculous.My take offs were sluggish and I was only getting about 12 miles per gallon.I was not happy with the performance and so I was ready for a change.It cost me close to $400.00The car is more responsive and I gained another 3 to 4 miles per gallon.Those plugs may last 150,000 miles but they don't perform at 100% for the entire 150,000 miles.If you live in the city I would recommend opting for the hotter plug when you change them to help cut down on carbon deposits in your tail pipe.

Thanks for the write-up.