So I decided to look up the 300W and 500W fans data to see how they might compare to the 835W fan in performance. (Also, I corrected the exact model of fan in the PDF attachment to the original post.)

Performance data here:

https://www.spalautomotive.com/documents/20182/94723/brushless_catalogue.pdf/
Here is an analytical breakdown:

Given that I am seeing about 58.4 amps running amperage at max RPM (14.25V at the connector), I am likely getting around 2,850 CFM actual through the radiator at full power with a static pressure drop of about 210 Pa. This totals about 325 air watts per the chart.

Adjusting the static pressure drop for the 74% area ratio of the 16" to the 18" fan and the change in air FPM, the 16" fan should get around 1,770 CFM at around 150 Pa. Using the fan affinity laws, assuming the 300W and 500W models are similar designs, the 300W model should get around 1,500 CFM at around 105 Pa.

So that means the bigger fan is getting almost double the airflow of the 300W fan, and about an extra 60% airflow on top of the 500W fan. Also, taking into account the increase in radiator area cooled, and the increase in cooling capacity ends up being quite significant.

If you account for the steady-state heat rejection of the air conditioner, then it becomes even more significant for engine cooling. Let's assume the air conditioner rejects 36,000 BTU/h on high on a very hot day. At a maximum ITD of 50 degrees for all coolers combined, this leaves you with 45,000 BTU/h rejection capacity remaining on the 300W fan. But with the 850 watt fan, you have 118,000 BTU/h of rejection capacity left for the radiator. So even though your airflow didn't quite double, your engine can reject more than 3x as much heat.

118,000 BTU/h is equivalent to about 46 horsepower hours per hour, or simply 46 horsepower. Using the old rule of thumb that heat rejected is about equal to power produced, this means you could burn fuel as fast as you would on the freeway, while parked with the AC on, and still not run out of cooling capacity.