I got a 4, with 31000 on it - on a 05 plate... cost me £4k.
No idea what to look out for, nothing has gone wrong with mine!
I had the first i believe, it had the green seats and had its own green exterior paint available (cyclone?). Other than the interior, i think it is just Dynamique spec.
I'm not sure what specs the others hand, but some had steel wheels so wondering if they were based on the Authentique.