Small hole. I drilled a 1/8" hole in the thermostat in a 97 GMC. It dramatically increased the warm-up time. If it was easier to get to, I'd replace the thermostat with one that has a much smaller hole. Use the smallest bit you can find at the local hardware store.

The thermostat opens at the specified temperature. If you install a 165° stat, the water temp will reach 165° before the water starts to circulate. Installing a 200° stat will keep your engine temp at least 200°.