I have a 2005 325 Xi and it has been worth every penny in winter. I put on snow tires for better grip when stopping, and it now completely rips through snow. But even without snow tires, it was great. The 2006 models have a much more advanced version of X-drive, so I imagine they are even better now in poor weather. Plus they are much faster now with the bigger engines, but I haven't really found mine to be much of an issue anyhow - plenty of power in the city when needed. I have driven both the 2006 330Xi and 325 Xi this summer, and they are both great cars.
Either choice is a good one.
