Yeah, 70 CFM seems right as a rough estimate - that's the neighborhood where the static pressure vs airflow curves for the fan and rad would intersect. If you look at the graph for your fan, notice the spot where airflow drops dramatically with only a slight increase in backpressure. That's where you're operating. A push-pull arrangement could make a big difference. Look for fans with high static pressure (closely packed fins on heater cores need higher pressure), focus less on their CFM rating.
Both probes are equally unreliable - subject to varying placement, contact pressure, changes in local airflow. On some forum, somewhere (can't recall), I saw a mod to allow the NF7 to read the thermal diode. That, or a variation based on the readers MMZ_Timelord is making, would a better temperature indication.
I'd try more air before changing the rad.
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