17" is the largest I'd like to go for a winter set. I've also been checking the local classified sites, but everyone seems to only be selling those thin, five-spoke designs that leave too much of the brakes exposed. If a 16" wheel could fit, this would increase my selection.
Since you are considering BMW wheels, do you know if the center bores are the same, or would we need centering rings?
Also, I have read (maybe even on this site) that some BMW years used a very low offset. This would cause the wheels to stick out on our Buicks with a more common FWD offset, which I think is either 40 mm or 35 mm.