yeah it's all about the merge. every morning I have to merge into a solid wall of 6 lanes (that's 6 lanes going each way) of traffic going between 60 and 80mph. 100kph is 62mph, don't remember how to convert the two. I also have to merge, on my way back from work, into 3 lanes of traffic that is going abut 70mph. And lets not forget all of those times you get stuck behind a large buss that's going about 50 and you have to reeeeeeally quickly jump over a lane and get up to about 70mph so that the big semi that's comming doesnt squash you. and of course lets not forget the 4 lanes (traffic going both ways- 2 lanes each) going about 50mph that I must dart accross on my way homw. and then there's the 2 lanes heading about 50 that I have to cross in order to get to the 2 lanes heading the opposite direction and once I'm there I have to make an IMMEDIATE 90 degree turn and be going 40 so as not to get squashed by the cars comming up behind me. this is just my home-work-home commute that I must do every day. And, my Honda 4-cyl gets about the same gas mileage, or less, than a 3.25L V6 325i. I test-drove a 3.28L 328i recently and had to merge in front of a truck that, had I been in my Honda, would have definitely squashed me. As it was, the bimmer barely managed to squeeze into possition.
edit:
lets not forget the primary factor of buying a fast car- FUN! You must not have ever driven a fast car. Go testdrive a Porsche 911 and you'll see why people like big engines on small cars. Relax, test driving it doesnt mean you have to buy it. Consider it free entertainment!