i used to do only 3k intervals with both syn and dino, now i push dino to at least 5k with mostly freeway driving, and i push syn to at least 10k with mostly freeway, synblend is anywhere in between. oils, i mainly stick to chevron supreme for good and inexpensive dino, mobil clean 5000/7500 for a good synblend (what i get depends on whats on sale, 7500 has more syn and more add pack), and mobil 1 or EP for syn. Sometimes i'll spring for GC when i find a good stash of it, and for oler cars/trucks i use mobil delvac 15w40, doesn't bog down like other HDEOs.