[gwnichol]

I use syntetics in my GTI because VW reccommends due to high temperatures caused by the turbo (coking can be a problem)and Castrol is the only manufacturer that makes it in 5w40 that VW reccomends. In ordinary climate and operating conditions mineral oil and synthetic work about the same. In the climate you're in and depending on how much stop and go driving you do a step up to synthetics might be worthwhile. Be aware you paying substantially more and may not derive much benefit. The oil manufacturers claim longer periods between oil changes but I'm not aware of any manufacturers that accept the extended oil change intervals unless synthetics are specified by the manufacturer. I know BMW does this. As far as weight goes the lower number is the cold temperature viscosity of the oil. Not really important in the warm climate you drive in. Your Owners manual should have a temperature/oil viscosity chart in it. You can't go wrong doing what the manufacturer reccomends.