cfm - I'm in the same boat as you... I've been leaning toward an xDrive, but I was concerned about the possibility of giving up a suspension more suited to sporty handling.
I've had both RWD and xi e46 3 series over the years, and I've learned the following:
- My 2000 e46 328Ci (RWD with DSC) was *astoundingly* good on Vermont's twisty snow covered roads with the stock Michelin all-season tires... far better than the front-wheel drive VW Corrado that it replaced. I was amazed, and wouldn't hesitate to recommend a RWD car with all season tires for snow country.
- In terms of performance driving, I have come to appreciate the tenacious grip that I get when getting on the gas early in a corner - particularly on wet or otherwise sketchy pavement. I presently own two AWD BMWs (an X5 and a 325xi); my X5 Sport has camber plates and a strut brace (among other mods), and it is unshakable in corners... the limiting factors are just the weight and the high CoG. The 325xi Sport has awesome grip too, but it would really benefit from a little stiffer suspension. I'd be very curious to see how track times of RWD and xDrive F30s would match up if the suspension firmness and ride height were the same.
So from my experience, I think you won't be giving up much either way, whichever option you choose.
For me, it's less a question of bad weather safety, and more a matter of which is the preferred driving dynamic for every day driving. I am literally headed to the dealer this evening to (yet again) drive xDrive and RWD models back-to-back to try to make my choice.