Mk2Reverie, I certainly don't fault you for trying to help others on here. Heck, that is what this place is all about.
But kind of hard to make such a claim knowing very little what the last owner did to your car. We all have our lapses or memory and who knows what they truly did as far as maintenance without any record.
At $110+ an oil change (04' V8 in an expensive city) I will be sticking to the 10K full synthetic, until someone convinces me otherwise.