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Or would that be MX5? Oh wait, that's a tiny little rear-wheel drive convertible from Japan. This is a big AWD luxury SUV from Bavaria. First Porsche "diluted" their brand by rolling out the Cayenne (though in Turbo guise, it's a hell of a truck) and for a while at least, they sold the hell out of them. This didn't go unnoticed by die volks at BMW. It looks as if Motor Authority has snagged some spy shots of what very well might be the Roundel's response, an M version of the X5. Note the dual-pipes. Engine speculation is rampant, but the uber truck could come complete with the screaming F1-derived 5.0-liter V10 out of the M5, or it could have a new twin-turbo 4.4-liter V8 good for a rumored 430 horses. Sounds fun, but would an X5 M be a dilution of the M brand? []