I don't know if Tom's one is the 460BHP version or not, but it's their unofficial gentleman's agreement with Ferrari. That and the fact that it's a Maserati grand tourer rather than an out and out circuit basher for outright speed. It's not trying to compete with any other car, because there isn't another car it needs to compete with in this segment. There's no reason why they could not have eeked 500BHP from the 4.7 v8 otherwise, considering the likes of Porsche can get 490 from N/A 6 cylinders at 4 litres.
Sorry forgot to say mines a 4.2