Well you live in CO so I assume you get your fair share of winter. In Ohio its not much different. The summers are fairly hot and the winters are pretty cold. The car actually seems to run smoother with the 0w30 than the 5w30.
Though I will say I'm not comparing apples to apples. The previous owner used conventional oil from what I could tell and a cheap oil filter(something no one should be cheap on).
I'll admit that I am thinking of switching to a heavier weight synthetic, just for the sake of comparison. But I won't switch from Mobil 1.
