There's a lot more going on than drive train loss. I recently went from a 2007 E92 328xi to a 2008 M3. The weight of the awd, tire wear in front, really heavy steering, all add up to a totally different feel, and a lot of stuff to push around.
Also, the 325 and 328 versions of the xi have slightly different final drive ratios: the i has a 3.73, and the xi has 3.91. The 330, 335 i/xi have the same ratios, all 3.73.