Atlanta is about like SC where I live. Average winter temperatures are highs in the 50s and lows around freezing. I have and will continue to use my bimmer with summer tires on it in these conditions as long as it is dry. If the temperature will be well above freezing, I will drive it in the wet in the winter, at these temperatures, too. I do not drive especially cautiously and I never see the stability control kicking on. I never see stability control unless I am in an autocross (where I generally run with the DTS in the partial off position). It's easier to trigger the stability control in the 135i due to the greater power. But I don't think tire compound makes much difference there either. Too heavy throttle is the issue, not the tires.
When I lived in Pittsburgh PA, Philadelphia, Omaha, and Kansas City, I drove on all season tires. I do not think summer tires are reasonable for daily drivers in these cities. On a nice winter day, they would be fine IMHO, but you cannot count on these conditions. In snow or potential icy conditions I would not advocate anybody driving on summer tires in cities this far or further north and I never have.
I used winter tires including with studs back in the days before radial tires. I think they were a good idea then but radials added traction to all sorts of tires. I believe all seasons are fine unless you regularly drive in deep snow. Then you need snow tires or chains. You give up some traction with all seasons but only in conditions where you should be driving carefully anyway. I've done it for decades including an occasional ~1,000 mile trip in the winter. They work fine, just remember they are not majic. With snow tires you could push slightly harder but would still need to be careful. Other traffic is very likely to slow you down to the point where all seasons in good shape will be fine.
But I still maintain that a car like mine, driven only on "nice days" in the winter is fine with summer tires in SC or points further south. Any difference in grip is undetectable even driving a little agressive on ramps. Tire rack has done good tests on slick conditions, however, and that is a very different story. Summer tires are just too limited. You need at least all seasons when the weather gets icy or there is significant snow on the ground. But for those of us in the South, waiting for it to melt is a valid option. It typically takes less than 24 hours. I just use my SUV (rear wheel drive with all seasons) when it gets bad out.
128i Convertible, MT, Alpine White, Black Top, Taupe Leatherette, Walnut, Sport
Ordered 5/22/09, Completed 6/4/09, At Port 6/9/09, On the Georgia Highway 6/13/09, Ship Arrived Charleston 6/24/09 at 10pm, PCD 7/21/09