A night of colossal boredom meets extreme nerdery has me reading more on oil.
Another reason I found to stick with 5W-20 over 0W-20 is the former will have a lower NOACK rating than the latter.
Essentially, the NOACK rating tests the volatility of engine oil. The lower the rating, the less oil that gets burnt off when it gets hot (the test heats the oil to 482 degrees F, holds it for an hour, then measures how much was lost).
This becomes critical in direct injection engines, as less volatility means less engine oil being put back into the intake manifolds. As we've seen here, direct injection engines can have a ton of buildup in the intake manifolds and valves. Anything to help cut back on that helps, and that includes sticking with 5w-20 oil.
Unfortunately, I haven't found much of a list of the NOACK ratings of 5W20 engine oils. Here's a chart for 5W30:
Here's an incomplete list of 5W20:
https://docs.google.com/spreadsheets/d/18I-xK-pJfhhYMdxC6bhx8cnBLhFZq0AM4a7BtyZzTfc/htmlview