As quality goes it depends of who made the replica. The main thing is that most replicas are not forged they are cast. This can decrease the toughness of the rim. Is it noticable......no. Is it going to really matter at all for you...... no. I bought a set of replica 17 inch rims from aaarims.com they are going on my car this weekend. I would look at aaarims.com and wheelexchange.com they both carry replica wheel and I know wheelexchange has some M3 replicas. Also jlevisw.com has some wheels too.
So the choice comes down to wheel size.
18's -look more bling, give a harsher ride, fill the wheelwells a bit more
17's -more confortable everyday ride, handle better than the 18's on our cars, don't fill the wheelwells as much though, still look real good.
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