you're talking about cold weather - synthetic, but dino 5w20 is fantastic in the cold, unless you're down to -45 or -50, maybe since it's hydrotreated group II+, I don't know, but I was changing oil yesterday, and the QS dino 5w20 poured way better than the QS synth 5w30. (I am running self-blend 5w25) So if ur manual calls for 5w20, don't worry about using synth. if not, (and mine doesn't, it calls for 30 weight), then blend ur own 5w25, it's close enough to 30 weight that ur engine will be protected. I will eventually published the UOA of the Impreza 2.5 flat four run with 5w25, after I've done a few cycles with this weight. So far, the engine runs really nice, and there is absolutely NO oil usage between 3500 mile changes (severe service in my manual, Canada is by definition severe service).