I've always just followed the manufacturers reccomendations. Why would you do anything else.? who knows the car better? I've had mazda 929 (370,000 miles), Nissan Maxima (273,000 miles - daughter totaled), Honda Accords (187,000 & still strong)... and all on regular pep boys oil. I've tried synthetics - absolutely NO difference in milage. It would appear to me that there is an unbelievable waste of oil in this country if people are changing their oil at 1500, then 3750 etc. instead of what the manufacturers are reccomending....7500. All of the above cars burned NO oil between changes and were sold/traded due to looks (rust) or accidents. I'm using the same oil for my new Accord Hybrid, and it's been performing above expectations...on my daily commutes ( 85 miles each way), I never get below 39 mpg, and up to 43.4 mpg occasionally.
hans