Cold weather diesel starting

Yes, I know, this topic has been done to death. But still...

What is the lowest temperature one can reasonably expect a 617 engine to 
start given new glow plugs and an average battery?

Dropped to 10 F. here yesterday. It would not start. Called road 
service. Guy showed up with a dinky booster battery pack, no jumper 
cables. Well, of course it would not start. It would barely turn over at 
all with that booster battery. Later in the day when it was slightly 
warmer, we called road service again and this time he showed up with 
jumper cables. Took about thirty seconds to start.

Seems to me cold weather is a double whammy for a diesel. Even if the 
battery is in good shape at low temperatures it just does not have the 
capacity it does when warmer. So cranking runs it down  really fast. If 
you cycle the glow plugs several times you are depleting the battery so 
the heat from the plugs is canceled by inability to fast turn over, 
which is essential. A slow cranking engine just will not start, unlike a 
gasoline engine where a spark just might get it going even if it is 
cranking slowly.

So, below what temperature is starting a diesel in otherwise good shape 
problematical?