If I had a job like scenarshooter's where temp stability was a huge part of being successful in the field, I'd definitely look into using Varget. But, I also found that '15 was pretty resistant when shooting it around 0 degrees and snowing like a mofo (calling SamO).

Guess it just comes down to which way your dong hangs.

FWIW, '15 pushed 178s around 2740 in my 26" 308.