This is my 7th BMW and currently my "winter BMW." I drive a Z4 3.0 most of the year (with Dunlop winter tires for the winter: just in case I'm caught out without the X3). The X3 drives like the last 3 series sedan I owned (325i) and totally unlike any SUV. The stock Pirelli all season tires are somewhat of a compromise in the snow and on ice, but the X drive makes up for it. The trade-off is the dry weather handling, which is "standard 3 series." I would not consider the 18" wheels, because of all the reports I've read and the fact that there are too many pot holes in Mass waiting to bend big rims. If you want a great combo, go for the Z4 and X3, which will exceed any one car's performance.
X-drive, 3.0 engine, great bad weather performance and real BMW handling.