I believe the Z8's are good for low 13's, I think the 13.1 range. They have the M5's 5.0L 400hp engine.
I guess I am lucky because I get to drive a Z8 every once in a while. They are just plain kick *** cars (even if you are only going 15mph
) But you really have to be a huge bimmer fan to buy one. For that kind of money, I would go with something a little more agressive looking/performing, like a Ferrari.