From Auto Express in UK:

Watch out Porsche Cayenne! This mighty machine is BMW's X5 M – a range-topping performance flagship SUV that boasts a twin-turbocharged 4.4-litre V8 producing around 500bhp.

Targeting the Cayenne and other hot SUVs like Mercedes' ML63 AMG, the new model goes on sale later this year. Development is gathering pace as this prototype, which was spied undergoing winter testing, shows. With quad exhaust pipes, covered-over M-style side vents and larger frontal air-intakes, it's clearly no ordinary X5.

The finished version will carry a host of M-badging too, and along with the prodigious powerplant – which should rocket the SUV from 0-60mph in around five seconds – the newcomer will get stiffened and lowered suspension, uprated brakes plus wider tyres.

Expect a price tag of around £60,000 when sales start later this year with a similarly powerful, X6 M arriving in 2010.