I'm in the same situation, and drove both the 328 and 335 today. The 328 is definitely more lively and responsive than I expected. They didn't have a 335 Msport on the lot, so I drove a sport 335. Shocked that the six gets the same mileage as the four, I definitely think I'd go with the Six, although I haven't figured out how much more it'll cost me (yet).
Funny thing is the dealer gave me the 328 for the night, and as expected, I've been pretty impressed by it. Now I'm stressing over whether its worth holding out for the 335 or just pull the trigger on the beautiful 328 sleeping in my garage tonight.
The dealer would have to do a pull-ahead on my E93 335, and I owe 4 more payments, so I doubt the deal, as I presented, will go through anyway, but its a good exercise to force me to evaluate 328 vs. 335. . .