Doesn't matter synth or dino as far as being thinner. They meet the same specs. The 5W means it flows a bit better in colder weather, for cold starts, so should be good for winter. 10W is slightly thicker when cold. The 30W is what is at operating temp. I use the Mobile 5W30 year round. How long it lasts depends on a lot of factors. If you are running too rich, or doing a lot of short term driving to where the fuel mixture is running rich because it hasn't warmed up and getting fuel into the oil, or if you do a lot of short driving in the winter where the oil never gets hot enought to expel the excess moisture your oil will contaminate sooner.