Do NOT run 20-50 weight in these engines, the hydraulic lash adjusters are not designed to run this thick of oil and will cause them to not be able to bleed down correctly. Also with the tight tolerences of this engine can cause oil starvation to certain parts expecially at high rpm
Please stick to 5-20, 5-30, 0-20, 0-30 weights
"So, do people who use 5w-20 run into these issues @ 50F? That's when a 5w-20 is heavier than a 20w-50 @ 100F. They're equal @ about 95F (95f for the 20w-50 and 50F for the 5w-20 -if I used the visc calc correctly)"
I am little confused by your calculation. Since the viscosity is figured at 32 degree's for the "winter" weight (5 vs 20 weight) and 212 degree's Fahrenheit ( 20 vs 50 weight), I don't see how a 5w-20 can be thicker then the 20w-50 weight at any same given temp.