I'm not really sure what you are trying to figure out but I own a 2004 325xi which I picked up in europe(american specs) I loved this car it kicks a__!! I live in North Dakota so if you want tp put this car to the test this is the place to do it because of the extreme winters! It handles great in the snow and ice and the DSC kicks in the second the car feels you sliding or your tires spinning. I had no trouble starting this car at temperatures well below -70 F. I chose this car instead of the 330 because it's a few thousand dollars cheaper and I really don't need those extra horses that the 330 gives you. The only complaint I have with my car is that I wish the trunk was bigger because a suite case barely fits.
330 vs 325 the difference is some extra options, and a little more horse power, so it's up to you what's important. For me was the extra cash in my pocket. If I wanted to race I wouldn't have bought this car I would have gone with the 330. Don't get me wrong the 325 is very fast but is not a race car. I hope this helps a bit. The only thing that I heard about changing the tires is that you should at least do it in pairs.