06 Legacy 2.5i: GC or PU for winter?

[bodeh6]

1. 2006 Subaru Legacy 2.5i (52K Miles, Auto, Naturally Aspirated, stock)
2. SM/SL 5w30 but lists bunch of other weights up to 20W-50
3. Metro Detroit, MI. Winters can be 0-30 degrees Fahrenheit with lots of snow.
4. Moderate Driving. Redline a couple of times per day while driving
5. Work is 12-15 Miles away, 75% Highway 75-80MPH. Rural streets 45-50MPH.
6. No Problems.

Current fill is SynPower 5w30. Last winter was my first run of synthetic with QS UD 5w30. Already have a jug of Pennzoil Ultra 5w30 in the stash. Will probably be due for an oil Change around late Dec/early Jan. What would be better for winter German Castrol 0w30 or Ultra 5w30? Only issue during winter is a knocking noise heard when I first turn on the car in cold weather, goes away after warmed up a little which is a characteristic of the Subaru boxer engine I hear on the web. I park outside so sometimes it is covered in snow from an overnight storm. I would buy the GC when Autozone/Pepboys put it on special again as both around here carry it all the time.

 

[5sfe91]

I would use the PU and even Castrol EDGE 5w30 would be a good choice since its on the thin side

 

[chet2]

ultra

 

[ChiTDI]

I've used GC for eight Chicago winters in a Toyota without incident. Having said that, I would think the Ultra has better cold temp properties and would use that in your situation.
(In the correct grade).

 

[meep]

my 2.2L loved the slightly thicker side in DC area. 10-30M1 year around. 5-30 would shear and get noisy by 2500 miles. I ran 10,000 OCI and never had any problems. I dunno if I'd worry about getting the thinnest oil. I think either choice would be fine, but also that piston slap, which mine had too and never caused any problems, would be a little happier with the slightly thicker oil.