I haven't driven a 335i in any form but I have driven a 320d Saloon and a 320d Convertible, both Auto's with the 184 BHP engine and both over the course of a few days (so not a quick 20min test drive)
All I will say is you certainly felt the extra weight in the Convertible everywhere but mainly on acceleration, the Saloon felt like a rocket when you floored it but the Convertible felt very Mercedes like so to speak and bit dull in corners, but it was bloody lovely to have the roof down in the summer and people having a good look at the car
End of each quarter is the best time to buy a car as they need to hit targets and will bend over to get your business