There is absolutely no reason for you to buy a 335d with that sort of annual mileage, the 335i is clearly the obvious candidate here.
With a 335, M Sport v SE is purely down to personal preference over the way the cars look as this is the ONLY real difference. All the important M Sport additions like seats and suspension are standard on all 335i regardless of trim level.
Pre 57 plate cars are not Efficient Dynamics cars and are therefore taxed at £440. Later ones have better economy and lower emissions but power and torque remains the same.
Peerzy is talking rubbish in saying that almost all 2007 cars are under 3 year warranty - we've only got 3 months left of 2007 so 75% of 2007 cars are therefore over 3 years old!
Do not buy one without a warranty. They are complicated cars and the potential for large bills is great. The high pressure fuel pumps are a particular bugbear, and there are stories of turbocharger failure as well. A warranty is a very sensible idea.
Buying from BMW gets you the best warranty you can get but don't be fooled into thinking it will be the best car you can get. It will be like any other car, only with a great warranty. The cosmetic condition etc etc of many AUC's is often not what you'd expect. Only pay a premium for the warranty - it isnt worth paying the premium for any other part of the AUC experience.
The one you've found at Sytner is a good price but there are two important buts with it:
a) It has the most dreary, boring interior combo available and makes the interior look very plain
but more importantly...
b) It has 70k.
Now you may be suprised to hear me mentioning mileage as a negative aspect but its important. Mechanically and cosmetically the mileage will make little difference but value wise it will make a big difference. The closer you get to 100k miles the harder this car will be to sell for good money. This matters when you are paying almost £20,000 for the car and this is why this car is priced keenly as Sytner know it has a limited audience at this mileage. Also check the condition, as I said not every AUC is mint - I had a nosey at a local 335i and was suprised to find quite deep scratches in the paint
As long as you are happy that you will lose perhaps £10k on this car on 3-4 years, then great.
One more thing..
To me, the appeal of a 335i is that its a fantastic all rounder. You already have another vehicle for day to day useage and therefore your car is simply a toy.
With this in mind, is an all rounder like a 335i really the right choice? Would you not prefer something a little less practical and a little more ridiculous? I will probably end up going the 335i route but it will be my only car and the reason I like it is because its as good at the daily grind and driving up the Motorway as it is at putting a smile on your face. This isn't part of your usage profile, mind.
It's very different to something like a VXR8. A better car, for sure, but a better toy?