Opportunity's experience in the sand came in handy in October 2005, when NASA detected unusual traction problems on Sol 603. (space.com)
Yes it'll be noticably slower than and M5, but I believe it's still plenty enough for road, and you also get less traction problems. (evo.co.uk)
Funny how this received 4 * despite the unsurprising traction problems and yet the Lexus 450H received a perfect review in what is a comfort orientated specification, costs around # 10k less than the competition but scores only 3.5 *. (autocar.co.uk)