Right then, this is easy peasy. I have just upgraded from an E39 530D to an E61 535D m sport touring. I think the best way to describe this machine is OMFG........ 4 weeks in and Im still grinning like a Cheshire Cat everytime I squeeze that right pedal. Its an awesome drive, totally effortless power and so refined, I must admit the build quality is not quite up to the E39 but who cares. My buying tip.. IMO its important to find the right car whether it private or trade, if its not been looked after and loved... WALK AWAY.... main dealers will offer great warranty etc but you are gonna pay for it on the price of the car. In addition Im pretty sure you will struggle to find an 06 plate in the dealers. If you buy a pre 07 LCI you'd be advised to have the swirl flaps removed, (engine fatality if one breaks), Camshaft sensors are prone to fail as are the rubber vacuum pipes from the turbos (these are reletively cheap fixes). Try are get a post 07LCI with more miles these engines are fantastic but if problems do arise they tend to be with age rather than milage. Gearboxes are bulletproof. Runflat tyres are expensive to replace and alot dont like them but thats another story. Finally, get a good spec. If you dont your going to be putting your hand deep in your pocket for upgrades. I set myself a minimum of Pro Satnav, heated leather, media pack (bluetooth phone and AUX USB ports). Good luck with your search. If you fing one, make sure you post again, I guarantee you'll be smiling like a little kid in the sweet shop.