As most have said, in an ideal world 5w50 is equal or better under all circumstances than hte 20w50. But this world is not ideal. I bet if you look at the specs for reach, you will find that, while both are "50" weight at high temps, the 5w50 is not as heat stable as the 20w50. I suspect they also had to use or use more viscostiy extenders ("VIIs")to make the 5w50, which has several side effects.
If this is for light use and short change intervals it may not matter.
I also ask why such heavy oil. heavy isn't better, its just better under very high temperatures.
Quick update: I grabbed the 100 deg C CSt (viscosity) for edge 5w30 and 10w30. Both 30, should be the same right? No. 10.7 vs 11.3. QED.
But in the long run, who cares, both are fine so long as you dont race or leave them in tooooo long.
With very long intervals, the 20/50 likely better -- but it wont flow well in moderate to cold.
G
