What you will notice is your warm up time will be extended and your fuel mileage will decrease if you drive short trips.
The final temperature will end up about the same as before you drilled it.
It'* mainly a racing trick that allows a cooler engine for a longer time....while waiting in the staging lanes.
Because of my shorter trips, when I tried 4 holes, the engine was failing to reach operating temperature and would throw a code and trigger the SES light...the newer cars are programmed to detect a thermostat that is stuck open.
ZZP sells a modified engine coolant temperture sensor that will trick the computer and allow you to run with even a 4 holed stat.
I now have only one hole drilled in mine and it works fine without the tricked sensor.
Two holes may also work. The pre-00 cars are less sensitive to this mod.