I guess your talking about the 330Ci ZHP? thus, the 235hp.
Well, i am not too familiar with the american Standard acceleration procedure, however here in Australia the BMW 330Ci with 6-speed manual (here in OZ, we don't get the detuned 225hp or the performance 235hp upgrade, we only have the standard 231hp, which is almost insignificant difference to the performance model).
The 330Ci here does 14.8 seconds for the quater mile (400 metres). This figure is based on the testing procedure of: 2 occupants on board and at least hallf a tank full. The figure i mentioned is with the 5-speed manual. I have not seen any performance figures with the 6-speed manual/SMG. However technically speaking, the 6-speed gearbox is actually taller geared, and 6th gear is more or less an economy gear. So I don't believe there should be any advantage with the 6-speed.