I love my stock OEM continental cross contacts that came with the DS.
It is very similar to my Continental DWS (now it's called -'06) for better grip in a wet, snow, and light ice conditions my BMW X5 diesel goes thru.
I ditched the stock run flat BMW tires as soon as I got them and have been driving the Continental DWS for 3 years now and loving them.
I had the Conti DWS when I had the BMW 335d as well and loved the grip, quiet ride, and softer sidewall than the stiff RFT.
The DWS tires are great - the tread has the letters in different depths to indicate condition to drive.
In the rubber and when you can see all the letters -DWS then it can go anywhere - dry, wet, snow. When it wears down and you can only read DW then it is wet and dry rated. When you can only see D then it is dry pavement only and time to change out....
Try Tire Rack online and see what they suggest - they have a huge selection of great all seasons.
Here are my Conti DWS on 20" BMW rims: