Testing Coastal Full Synthetic

After a using 10w-30 and 40 dino oils at 3-4k OCI's the entire life of the car, I saw Coastal's Full Synthetic for $3.59 a quart and decided to try it. The car is a VW Jetta with a 2.0 8v stock and 117K miles. The introduction of this synthetic was right after the injectors and engine was cleaned with kero and diesel, and so the engine is very clean now. I understand from this website that Coastal has been called a group III product. What OIC interval would you recommend for a UOA, as there are no other findings here?