Thanks so much for all the replies - loads to start thinking about there. I think it has to be a 240, something about the style of them that we both like - even if the 7s and 9s might have plusses that we'd lose out on.
Insurance is a real issue these days, so I think turbo will be out of the question and we'll be looking for something that's cheaper, but hopefully not underpowered (and fuel injection comment taken on board). Getting my head around how insurance works is beyond me, though.
Trying to get decent mpg will be a good challenge for him - tuning as well as possible, driving carefully. And I think if we can find the right car, loss of some money on petrol (he won't be doing anything like high mileage) might be offset by the overall investment in a beautiful car that's going to appreciate with both work and time.
I know he's trawling the net as we write, and he's following this thread - we really appreciate your comments and, once we find the right car, will be back to bother you with endless questions, no doubt!
