I am running MS controlled MPEFI on a 480ci Hemi '69 B-body.
Edelbrock intake with 2x1000 cfm throttle bodies, with the IAT sensor originally in the air cleaner base between the throttle bodies.

I had the Ramcharger ductwork off the hood for a while. The IAT ran 60 degrees or so above ambient.

With the ductwork on and a good seal to the air cleaner, on the road IAT went to about 10 degrees above ambient.

Air temps 11 degrees cooler offer a potential HP gain of about 1% -assuming the mixture is corrected for the temp change.

As a sidenote, getting meaningful IAT is not easy. I dealt with sensor heatsoak issues on hot restarts. Moving the IAT sensor into the ductwork and modifying the sensor transfer function table cleared it up.