Not sure what you find "slow" about the car. Perhaps you are expecting some kind of Turbo kick? Instead you just go fast without any fuss. If you are used to the turbo kick from other cars, you won't find it here.
I don't know if your previous cooper was modded but the 328i should be faster.
2013 BMW 328i Sport - Back in the family!
2007 Honda Civic Si Sedan (Retired, Meh)
2005 Infiniti G35 Coupe 6MT (Retired, great car)
2002 325xi (Retired, very much missed)