As said the 335i is not in the same league as the m3 infact I'd say the non m cars e90 chassis is one of the worst they've built. take the 335 to birds for the bushings, diff, arbs and suspension along with the big horse conversion and you could of bought the m3 in the first place. I looked in to doing it with my old one as I couldn't live with its floppy handling but the cost of the conversion could of bought me another car so I traded it back in for another edition 30.
The M is in a different league and would be a great choice as long as petrol costs are not to much of an issue for you
And the dct box is meant to be very good so I hear - only been in a manual ( remapped ) and tbh I loved it.
It's a shame though I've had an e30 M3 ( 3rd car when I was 20 ) e36 m3 Evo and the e46 M3 and was really looking forward to owning an e9* one day, but sadly it's thirst for fuel is too rich for my blood !