Guys,
A sincere thank you for your replies. In my Volvo hand book on page 7:9, it says to change the engine oil and filter every 10,000 miles or once per year, or, every 5,000 miles or 6 months, if the car is used under severe driving conditions. e.g. extreeme temtratures, towing, prolonged high speeds, etc.
My Haynes manual says on page 1.2 to change the oil and filter every 10,000 miles or once a year, whichever comes first. If synthetic oil is so good, why should it have to be changed every 5,000 miles? Apologies if I appear dumb, but I'd like to be clear in my mind about this before I change over, as I've never used synth oil.
Again, thank you for your time and effort in putting my mind at ease.