I believe you're overthinking it. Just run the factory recommended interval with your favorite oil of choice and you'll be fine, like the others have said, the deposits you see under the cap are just that, under the cap. If you had that much junk in the motor it would have probably seized by now. The shop I used to work at regularly serviced a customers' Sienna van with the same engine that had ran bulk 5W-30 and less than quality Purolator jobber filters all it's life pushing 400k on the clock. Had the same gunky buildup under the cap, too. Pennzoil conventional is a good at cleaning and keeping things clean. Although, you might consider Pennzoil Platinum in high mileage flavor. There's no realistic need to run an oversize filter either, as long as it's changed often it won't make a difference the size of the filter.