My first UOA on the dexos1 AC Delco 5W-30 came back after 4200 miles looking quite hale and hearty. The OLM says I could do 6000 miles, and Blackstone agreed; the dealer recommends 5000 no matter what the OLM says. So once my CPO oil changes are over, I'm going to shoot for 4500-5000 on a dexos1 synthetic and not worry. Your turbo is in another class entirely, and a synthetic might well be called for anyway, esp. in your climate.