There are tons of posts about this in Factory Forced Induction. The Subaru Rally team uses Motul Synthetic, and the consensus of the posts in FFI settle on Motul as the preferred motor oil.
Do a search, and check out:
http://www.i-club.com/forums/showthr...ighlight=Mobil
http://www.i-club.com/forums/showthr...ighlight=Motul
http://www.i-club.com/forums/showthr...ighlight=Motul
http://www.i-club.com/forums/showthr...ighlight=Motul
Also, you'll notice a trend of WRX people leaving Mobil 1, as the new blend, SuperSyn, is apparently of lower quality, yet they're still charging the same prices for it, which some peeps feel may be a ploy to boost their bottom line. Not to disparage Mobil 1, as it is still a great oil (it's in my car right now, in fact!
).
At my next oil change I'm switching to Motul 300v 5w40 until November or December, when I'll use a 5w30 oil.