How Much IAT is Too Much?

L76, supercharged. Running E38 ECM, so no provisions for ECM intercooler fan ctrl.
Looking at setting up a intercooler temp switch to trigger a separate "push" fan and therefore the question. What would be an acceptable IAT before the aux fan triggers 110F, 120F?and off at 90F?....understand this will likely only be when vehicle not in motion- no frontal airflow
note: IAT reads of LID but trigger will be on intercooler coolant line.

The intercooler pump is always on and the temp this time of the year stays cool but fear that in summer it will creep up into the red..... causing all sorts of problems.
any suggestions