:Sigh:
5W20 is fine for summer. xWy oils are "multi-viscosity" blends. A 0W20 is formulated to flow like a 0 weight oil when cold, but like a 20 weight oil at operating temperature. A 5W20 flows like a 5 weight when cold, and like a 20 weight at operating temperature. In other words, for 98 percent of the time the engine won't see any difference whatsoever.
The shift to lighter weights on the low end of the multi-vis spectrum is driven by two things: One, the manufacturers want the oil to flow a little better under VERY cold conditions. Second, and IMHO more important, they're getting hammered to improve fleet fuel mileage, and thinner oil lets the engine spin over just a tad better when cold.
Personally, I run 0W20 in the winter (December through February) if I can find it, otherwise I run 5W20 and never look back. For summer I might run 5W20, or I might run 10W30 or even 10W40. Getting oil to the bearings when it's 75 degrees overnight is MUCH less of a problem than thin oil for hours straight on the highway at high RPM.