Based on your other cars, I would seriously consider the E55. Don't get me wrong, I love the M% and hope to upgrade my 540-6sp to one someday, but the major appeal of the M5 is that is a seriously fast car that offers a manual and can still carry four adults to the club. However, you already have other, more purpose built sprts cars, so the M5 seems like a bit too much overlap. The E55 is still quite fast, but in my opinion, a bit more versatile with a larger back seat and smooth automatic transmission. Personally, I like the looks and ergonomics of BMWs better, not to mention the larger percentage of enthusiatic drivers, but in your case is seem like the E55 may be a better choice. Happy shopping!