I just follow the mfg's reccomendation and change my oil every 7500mi. However, I do use Mobil 1 10w30 with either an oem or mobil 1 filter.

Our family's mercedes has a "flexable service schedule" indicator, which counts down the miles to the next service, based on driving habits, milage, and time. It goes for about 10,000mi+ intervals on synthetic oil.

not all cars use 5qts. my accord uses 4.5 qt with a filter change. our old school 85 benz with a v8 uses 8qts. german cars usually have a remote filter, located just ahead of the cylinder block, accounting for some of the increased oil capacity.