Fellow listers:
Synthetic oil is the best. 
It was first developed during WW II by the nazis while in Russia. It was so cold that the German tanks would not turn over because of the regular oil being so thick from the ultra freezing conditions. That is when it was developed by the German scientists because of it's unique capabilities.

Somewhere between 7 and 15000 miles is the perfect time to make the change however if there are any potential leaks this oil will find them and a leak may develop.

Many top of the line foreign cars such as Porsche now come from the factory with synthetic oil already in them. It is also used by many major airlines . 

One of the most important  advantages of synthetic oil is it's ability to protect engines under extreme heat conditions and we all know that heat is what kills an engine.

Besides my  1990 Westy multi I drive a 1989 Benz 560 SEC.  a 1967 Ford F 100 pick up, a Nisson 300 ZX and a 1995 K-1100 BMW motorcycle All use synthetic motor oil. The Bike has  synthetics in the engine, trany and rear end.

If you normally change oil every 3 or 4 thousand miles synthetics might not have any short term gains but in the long run your engine will last longer and if it happens that you vehicle does over heat the synthetics will handle it better.

Clarence 
Pinehurst, NC.