With factory fuel injected small blocks GM thought 220* was the upper "normal" limit. I haven't done any math on it, whether it actually would help or not, I like to keep the temperature swings a bit tighter, just in case thermal expansion is somehow critical in those ranges. It can't hurt to keep temps more stable.
195* was pretty much the standard factory GM thermostat temp since the start of emissions...very few GM's were prone to overheating in factory conditions. Doesn't mean you can't do better than they did, but also doesn't mean a lower temperature thermostat should be necessary to keep an engines temp under control for most applications. Crawling in extreme heat with big tires, big engine, stacked coolers and wanting effective AC is going to need an effective cooling setup.
Don't forget...the thermostat is there to set MINIMUM engine temperature. Once it's open, the cooling fan, radiator and water pump are the only things you've got to keep temperatures from increasing. Lower temp thermostats do nothing for overheating, except potentially giving you a bit more time before engine temps are higher than you want. Whether a thermostat opens at 160* or 195* has zero bearing on the engine getting to 215*...at best, only how long it takes to reach that temp.
Physics does not bear out the coolant moving too fast theory. There is one instance that trying to move coolant too fast can cause issues. If the pump cavitates, which isn't likely for those spinning pumps at "normal" engine speeds. Very simple way to look at it...if system A pushes all coolant through the radiator once a minute, and system B pushes all coolant through the radiator twice in one minute, you've effectively doubled the size of the radiator assuming you can shed the heat. That's for the fan/airflow over the radiator to handle.
Also note that the cutouts in the core support are nowhere near as large as the radiator itself, especially when looking at big block and diesel radiators, meaning coolant capacity is likely a valid consideration as well.
Stagnant coolant boils immediately against the hottest engine metal. Also, radiator cap needs to be functioning properly. Pressure is what really raises the boiling point of your coolant, boiling coolant is not good. Little sleight of hand from the coolant manufacturers...yes, antifreeze raises the boiling point, but nowhere near what your radiator cap does.
The colder coolant starts out, the faster (and more) it can absorb heat. Slowing coolant down does what? Raises coolant temp in the engine (leading to boiling), thus decreasing rate of heat absorption, ability to absorb heat, and how much heat it can absorb. Its not as simple as more heat absorbed = better.
As mentioned before, idle temperature issues are almost certainly airflow. A mechanical fan may be rated at 5000CFM, but at what RPM? Probably NOT idle. A single speed electric fan is whatever CFM it's rated at, independent of engine speed.
Having gone with an LT1 electric fan setup (likely nowhere near as effective as the Windstar fans based on overall size) The primary fan is enough to cool the engine in any condition I've been in thus far. Yes, minimal heat load (Vortec 350, manual trans, no AC, cheap parts store aluminum K5 radiator replacement), however that single little fan has no problem keeping up while pulling a trailer up steep grades or logging roads at 95*. It's still pretty impressive to watch the needle move down when that little fan comes on.
With the proven Windstar fan setup, you'd probably be hard pressed to get better idle cooling from another near drop in replacement.
And the one caveat, as someone always has different experiences: there are a lot of variables at play, people see different results for seemingly unexplained reasons.
. For example, it's 58 degrees here now, all the engines run cool, A/C is more efficient and the engine makes more power, so win/win.
