I have had great luck with Mobile 1 (I also ran Amsoil until they came out with the o-40 Mobile 1). I run 0-40 in my 150K miles 525i, If it's not too hot you might want to start with that.
Conventional oil is too expensive to run.....every 3K miles plus a filter and disposal....no way. With Mobile 1 or other reasonable synthetic, you can extend your oil changes and add a quart and a filter along the way if 5 to 10 K oil changes bother you...