The 335xi has the X-drive system, which is roughly equivalent to AWD. The 335i is a RWD car. For a lot of people (like me) an AWD car is seen as better in very snowy conditions. But I was told and I read in many places that a 335i with a good set of winter tires will do the job of keeping you safely on the road in winter.
You can expect to pay a premium of about $3000 for the 335xi over the 335i.
I suspect the winters in the Carolinas do not compare with mine in Canada so I would suggest to go with the 335i, and buy a good set of winter tires with the $3000 you saved.
Go on the BMW USA web site and do a comparison of the 335i and 335xi for more information.