If your engine is in good health and starts quickly, and the glow plugs are all working, CCA's aren't really much of a concern. Remember that at 0˚F your battery will have roughly half of the capacity it has at summer temps. Better to make sure the engine is healthy and starts easily than fretting over how strong the battery is.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]