I would think the Redline 0W40 would be perfect(although, I haven't looked at the numbers on it.) 0W for the cold temperature starts and the SAE40 for better protection once it warms up. I would not track any 20 weight on sticky tires with these cars, especially also at those temps. Redline is good oil and has tested well, but if it breaks down, you're losing a lot of hydraulic protection on the bearings and journals.
Unfortunately, I haven't seen any data here on any of those specific oils in these cars.
You might be even be better off with the 0W40 over your current 5W30. Other than the slight HP loss from the 30 to 40, I don't see why not.
My 2¢, for what it's worth.

 

IMO redline is one of very few oils I would not recommend in most modern cars, including ours. Way too much calcium in their blend for my liking. I love it for older cars and highly recommend their trans\diff fluid. Just not motor oil on anything high compression and\or direct injected.

 

highly recommend their trans\diff fluid.

second that for the trans and diff

 

I still believe going up to a 40 is overkill for daily use. But if I had to choose ONLY between a 0w20 and a 0w40, I would take the 40 for sure in this case. Despite what people keep saying the cold flow performance between a 0w20 and 0w40 are not the same just because they start with 0. It just doesnt work that way. The 0w40 will be thicker in the cold. In fact it will usually be as thick as a typical 5w30 - 10w30 at and below 40c.
A lot of this depends on the oil pressure\temps you see. There comes a point where enough is enough and you just dont need or benefit from additional viscosity. I am a change the oil before and after a track day believer, so I would feel fine with a 0w40 on the track, but would never feed it to my BRZ on the street where I do 99% of my driving. If that is the way you choose to go, I honestly dont think the brand will matter much. Some will break down more than others, sure but at that visc level on this engine, I dont think any reputable 0w40 will shear down enough to worry about.

 

below 40c.

Just checking if typo?

 

All true. I just dont think most people realize how wide and overlapping those viscocity ratings can be. Try telling someone that a 10w30 and 0w40 may have identical viscosity curves between -35c and 40c and people dont believe it.
I cant say as to exactly how subaru oil pumps work other than the limited info I have come across online. But pumps used by many other manufacturers do have what is essentially a hard stop pressure relief valve on them. 100psi is a common setting as well. So it can happen when 100psi of oil feed pressure is achieved at times like cold start or too high rpm before warm up and while the pressure looks great the flow volume is reduced. Positive displacement is positive displacement, to a point.

 

All true. I just dont think most people realize how wide and overlapping those viscocity ratings can be. Try telling someone that a 10w30 and 0w40 may have identical viscosity curves between -35c and 40c and people dont believe it.
I cant say as to exactly how subaru oil pumps work other than the limited info I have come across online. But pumps used by many other manufacturers do have what is essentially a hard stop pressure relief valve on them. 100psi is a common setting as well. So it can happen when 100psi of oil feed pressure is achieved at times like cold start or too high rpm before warm up and while the pressure looks great the flow volume is reduced. Positive displacement is positive displacement, to a point.

The viscosity ranges definitely have some overlap like you said.

Out of curiosity, I just checked the peak pressure on my gauge and it says 113 PSI. It definitely jumps and stays above 100 during cold start for a couple dozen seconds until the revs die down. I'm on 0W-40.

Edit: 131 PSI.

 

60psi would be the lowest relief pressure I have seen. That wouldnt make sense for such a high RPM engine. 85-100 makes much more sense and is very common. If @vincentyang246 is correct that the pressure will read higher at the sensor input location, it is very possible that many of these thicker oils are overwhelming the PRV under cold conditions and experiencing high pressure \ low volume situations which cause excessive wear.

 

yeah the the relief valve is set to 60 PSI @ 88c using 5w-30. (measured at stock OE location). cold start doesnt work as well so you will see 100psi or more. even in low RPM.
pump is linear and so its oil pressure with rpm. up until 5k ish... the just flattens out. alot of people have published the data here.

OE location has a 5 psi Delta to top of oil galley if anyone is wondering too

 

Redline is a TRUE synthetic (Group V). Great stuff. I run Mobil 15W-40 only bc I get free oil changes every 5K miles. They fill it with 0W-20 wt which I immediately drain out.