Synthetics while being more uniform at a molecular level have the benefit of having much better detergent packages as well as anti-wear agents and generally more of them. That's why some people say synthetic causes leaks on older cars..... it's true, sort of. It's just that synthetic and all it's cleaners will wash away more crud inside your engine that a cheap oil probably wouldn't. Sometimes dislodged trash in an engine opens up where a gasket had failed anyhow and voila, a leak is formed.
My girlfriends 02 GTP is a perfect example. When I got it the engine looked like it was caked with mud inside ( literally, lol) because of neglect and LIM failure. Well about 14000 miles later at the last oil change I popped off the fill spout and looked around on the front head. The engine is cleaning up nicely inside and looks almost half respectable whereas before you couldn't see where the head bolts were as they were caked over. It also has a pretty severe oil pan gasket leak forming, but it actually was leaking when we bought the car.
I would use a good quality oil and run whatever you want for changes. I don't do the 3K crap anymore, it's a proven waste. Even at 15K when I sent my last analysis in on some oil from my old work truck it was still clean and was deemed serviceable. I generally change between 6K-10K nowdays and use a decent quality synthetic oil. That's just me though.