Re: 156 Diesels
I run a 20V 2.4, it's not mapped because I'm a bit wary about putting over 200 HP through a drive-train that wasn't really designed for it, but generally this is what I think:
The engine does make the car a bit nose-heavy, but the Veloce suspension keeps it all nicely under control. I'm not sure I'd fancy it without the uprated suspension but maybe someone else has an opinion on that.
I get well over 40 mpg out of it, £170 car tax and it still goes like stink, pulling like an express train from 1500 rpm to the 5000 rpm red-line.
If you drive your petrol Alfa up to the red-line all the time, you will probably miss that side of things although the diesel will be more reliable, probably won't throw its timing belt and won't completely destroy the engine if it does.
I love petrol Alfas, but whenever I get one as a courtesy car it's a real test of patience waiting to get it over 4000 rpm before it does anything. My 2.4 diesel will pull almost from idle and will outrun any petrol Alfa other than a V6 but some of the magic is missing.
Swings and roundabouts, really. Petrol or diesel, they both have something that the other doesn't offer, but you wouldn't get me out of my car for anything less than a 3.0 V6 or a GTA