I used to run W100 year round. Then I went missed on approach to my home field and had to divert to a nearby field. The plane was left outside with no heat in a TN winter. When I started it turned over slightly slower than normal, though it always tends to turn over the first revolution a little slow I guess due to my 10:1. The kicker though is when I sat there watching, waiting, for the oil pressure gauge to read something, anything...it took a long time. It was long enough that I considered shutting it down. From then on I switched to 20W50 in the winter.