I have been thinking, what's the big difference between cranking at -20f (5w) and -25 (10w)? My car will turn over with either at the lowest it gets here, 0 to -5f. A 10w oil may offer better film strength and dimension (cling?)than the 5w. At the expense of pumpability, a heavy film that does not drain down sounds good. Less VII is a bonus. 10w-30 M1, 10w-40 ACEA A3 might be good for long-term engine wear.