['68OrangeSunshine]

I live in AZ full time. I have a 4-tier core radiator on the 350 V8 in my '71 GMC Jimmy, and a 3-tier core in my '68 C/10 Stepside w/ 292 L6. [I'ts also the wider V8 style radiator, since the narrower L6 radiators became unavailable.] I use a 50/50 Prestone mix in both.
After some high heat issues on the 292, last summer, I flushed the system, put on new hoses and fresh coolant, and it runs fine. The 350 runs cool now too.
Can't remember what degree settings my thermostats are, but they're around 180 - 195*.
Too low a T-stat, and it just opens early, and the water sluices around, without spending time in the radiator to cool off.
For a moderate climate like VA, a 3-tier core might work. Four would be too much.