There are contributors more knowledgeable than me on this subject, but I am running a Big Block with what appears to be the same radiator/fan setup as you. I have not experienced any extended idle temperature issue using the conventional staged fan operation. I recently was stuck in a traffic jam on a 90 degree day and the temps stayed well in-check. Both fans were running, as expected when things got hot, but the staged fans seemed to maintain a consistant gauge temp. One caveat: I am using a thermo-controlled electric water pump.
It would be very easy to wire the fan relays to a single temperature sensor, but I don't know of any advantage in doing so.
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