I just purchased a Subaru Forester XT turbo. this is basically the same engine as used in the current WRX. The recommended oci is 3750 or 3.75 months to maintain warranty. The car will see a fair amount of California desert as well as occasional mountain pass climbing plus a lot of freeway and short trip stuff. I was thinking of Castrol GTX 5-30 for the price per gallon at Walmart and also because the change interval is so short. I don't really know whether the Subie turbo is hard on oil or not, the oil almost clear with the factory fill at 2500 miles. I would like to go synthetic but I am thinking with the short intervals it could be overkill. Any suggestions for my kind of service would be appreciated. I am a retired guy and won't be doing much drag racing.