if the engine was 235 with those radiator temps, I'd go back to the engine, when you get it hot, 210 is hot enough that the thermostat should be fully open, but maybe the fan control won't be full speed? that's above my paygrade. Certainly the fan should be full speed at 235.
Anyway, with the engine 210 or hotter, check the thermostat outlet going to the radiator, and the water pump inlet from the radiator. And check the block and head a couple places to see that the temps seem somewhat consistent.
At those temps, a water pump could start cavitating and drop cooling performance rapidly, especially with straight water and if the cap or system is not holding pressure. That could be what was happening with the engine 235, radiator 190 and 160. I'd be very careful that the system is holding pressure if running 210 with straight water, just do that for testing purposes. Old engine temp gauges would be graduated for the pressure of the radiator cap, red line was much lower if there was a lower pressure cap used. Straight water is less viscous, and has higher heat capacity than antifreeze, so it should cool better at operating temps, but overheat more suddenly at high temps.