It really depends on too many things. If all you do is city driving or a couple of miles to school or college there is no justification for having a massive engine other than as a penis extention.
Even if you do a lot of motorway driving, especially in the UK, a couple of litres is plenty to get you there quickly. You realise a 1.1 engine can do 70mph just as well as a 4.5 v8, right? And one of them won't need to stop at every second petrol station too.
Big engines are usually utterly pointless for road driving, and a seriously bad idea in this financial climate. In terms of insurance, I could've gone for the v6 version of my car without much of an increase (and sometimes I wish I had), but in my 1.5 I'll get well over 100 extra miles from my tank of fuel. The v6 makes a nicer noise though, I'd like that
Track driving and towing are the only reasons to have a big engine. And saying "ah has moar horsez!" of course. You don't need 300hp to go shopping or pick kids up from school. And if you were towing you'd surely go for a diesel instead, right?