a lot depends on the climate. I live in south texas and when it gets hot here the milage drops and there is a significant performance loss due to the hot air. If I remember correctly the new Nissan engines have variable timing and the computer will adjust to your driving habits. If you have a heavy foot naturally the car will get lower milage. If you put one of those stupid wings on the car you will loose milage and top speed, those things are just for looks. Most of the time the manufacturers expect you to shift at 3K. Non of us do this much since the power band doesn't hit good till about 4K. Synthetic oils are a bad idea for the break in of the engine because the seals and most importantly the rings might not seat well.