Pennzoil Platinum 5W-30 is 5100 cP @ -30C, and Valvoline Durablend(Syn Blend) is 4800 cP @ -30C.
I doubt that you would notice much of a difference in actual cold start performance at temps above zero for any GF-4/SM 5W-30 that is in the 5000 to 5800 cP range.
Of course, M1 will be at 4,000 cP or below, whatever the base oil group and a good choice for repeated starts in sub-zero weather.