My boss has a 4.2 quattro and its a stunning piece of kit, original owner was the guy who owns Weetabix !

I've converted a few 3.7 fwd and quattro models and my bosses 4.2, tbh there all roughly the same, 3.7 4wd isn't quite as punchy as the 4.2 but the fwd 3.7 goes about the same, although you can tell its fwd.

Spec wise, It depends what is on the car your looking for, some have built in sat nav and tv, different leather, electric eveything, options galore.

Electrics on my bosses have started to play up now, they are very costly to repair too so keep it in mind if you go for a fully specced model.

On gas I think he gets around 22mpg maybe more, so add a bit to that for petrol mpg.