What's the highest CCS # an engine could turnover?

M-1 posts that the pumpability of their oils are -37C and up, but at -20C the 15-50 is 5234 and it jumps to 14050 at -25C, so imagine what it is at [email protected]#$!? So I thought, what is the highest CCS number and engine can turnover? Is it differenct for different engines? Can it be so high that even though an oil is above the posted pumpability #, but an engine cannot turn over? How are the pumpability #'s calculated???