I just installed this a couple of days ago and did notice a 10-20C drop in oil temps in 70F ambients according to the oil temp gauge in the cluster.
However.....some other observations I made:
It does not take much longer at all to reach minimum oil temps at around 170F than before, but it does take quite a bit longer for oil temps to get into the 210F range.
I mention this because from what I understand, water and other combustion by-products end up in the crankcase and I think it's important that the water boils off and vaporizes at around 212F. So you would want your oil to eventually stabilize around that temperature.
After about 15 mins of cruising, my oil temps stabilized around 110C (230F) and pretty much stayed there in 75F ambients.
At night with 65F ambients it hung around 105C (221F) which is all good as far as I am concerned.
Today ambients hit 95F in my area and I was testing some meth nozzle changes and pulling a few datalogs. Spent about two hours on and off and oil temps held steady at 110C.
But on the cruise home - as I was taking it easy - I noticed that the open loop in the oil system finally seemed to hit a wall and was starting to heatsoak. Oil temps rose to 118C (244F) for the first time.
So overall I feel this is a great and cost effective mod, but I think that although it delays heatsoak in the oil system significantly, there seems to be a point where the system saturates in spite of the open loop to the oil cooler.
But this is after a couple of hours of driving in 90F ambients and even at heatsoak temps, it was still probably about 5F cooler than what the car used to run at on hot days.
Definitely worth it......but something I would remove in the winter for fear of oil temps not getting hot enough to vaporize water sitting in the crankcase.