I agree oil change alone is far from the only thing to check, I just got thinking after comparing the two and wondering which is more preferable just on that aspect. Both have third-party (dealer and local quick lube) verified service histories. They both seem to have been taken care of for the most part. One has slightly more miles but a few more options. They both will need some service/maintenance/repairs, but I was just wondering on the engine alone which is more preferable. I run synthetic on all my cars, and I have personally seen where it makes a difference (one example is spilling some on an exhaust pipe--the synthetic will stay there a lot longer and will continue smoking a lot longer, and clearly has a higher tolerance to heat).
The point about the oil filter capacity is well taken too. I use high efficiency/high capacity oil filters that are designed to go the mileage I run. I doubt the vehicle with the full synthetic oil changes used a high capacity filter, it was probably just the standard filter off the shelf for that model (which is actually a fairly high capacity cartridge filter, but probably not designed for 10k miles...).
Mostly I was just thinking out loud about the comparisons of 3-4k mile changes of conventional vs. 8-10k miles on a full synthetic change. The one main thing holding me back from deciding between them is that the one with the full synthetic changes has about 83k miles on it and the guy seems real eager to get rid of it. Problem with that is that he usually keeps his cars for 150-200k+ miles until they literally don't go anymore, and now it seems he is wanting to get rid of this one rather quickly for a newer version of the same model with less miles. Just makes me wonder if there is a large repair looming...
