Well here I go again. I believe that you should not extend oil changes because you are using synthetic.
I use both. I use Mobil One in my new V6, and I use a quality dino oil in my older cars.
Engines produce contaminants which find their way into the engine oil. This is why you change the engine oil, it's the only method you have to clean the engine internally. These contaminants find their way in there regardless of what oil you use. To get them out drain the oil, preferably hot and preferably often.
Mobil One is a great product, and I believe in it. But it can't slow down the contaminants that are produced by your engine.
Change oil hot and change oil often,
'01 C Class, Six Speed
'84 Euro 240D, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in