synthetic is the way to go, it flows better and is an oil designed for cars. if you were to do this in a beat up engine, the oil would likely find small holes to leak out of since it is thinner, but you are more than likely okay switching. there aren't any real benefits for our smaller non-performance cars, but it can't hurt. you could even switch to 50/50, or any other mix synth/conventional.
Rally Revolution #43