That's perfect.
If you use aquacomputer quadro or octo, you can monitor the delta, and make the fan's behaviour based on the delta.
Quite sure other tools allow it too.
Monitoring the delta, as you are, is the way to go. Only coolant isn't adequate, as during summer or even now with heating on, the coolant temperature could flag as high, but the delta not.
If your focus is on silence, a delta up to 10C is ok, as long your coolant doesn't get too hot to cause tubing issues. Mine always under 35C, but I'm happy to sacrifice a bit of noise for cooler temperatures. My OCD is more about lower than necessary temperatures.