I understood that the sport version (is?) was to be a twin-turbo V8 of 4.4 litres, with 400+ hp. If so, the move to turbocharging is consistent with the twin-turbo 3.0 I6 design philosophy, and is likely designed to keep weight down, add power, and avoid the corporate embarrassment of a gas-guzzling 5.0 (which may be OK in an M5, but would be too much of a bad-news target for a vehicle intended to reach a broader audience).

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue