Agree with fixed fan, no fan clutch for max airflow, but most power loss.
I think you are on the right track with the 3300 CFM electric setup, if it is an airflow issue. Had a mostly stock 75 Corvette in the shop that we wound up with a dual fan, one 14" and one 12" with properly modified shroud because of fitment issues, to finally keep it cool when extended idling, in gear, with A/C on. Calculated airflow was 4200 CFM.
I never ran a flex fan with a clutch, bolt directly to water pump with only enough spacer to clear fan belts, etc. Make sure you have proper spacing to shroud, if applicable. I have had best results with this type
https://www.amazon.com/Derale-17018-...s%2C139&sr=8-5
Short style water pump gets you an extra 1/2" clearance if you have a long style.