[Jfrahm]

Some thermostats have a "jiggle valve" for easier bleeding, which is a hole plugged with a small loose rivet that seals the hole under coolant flow. It allows air or coolant to pass through unless the coolant is moving, which forces the valve shut. I've bled 944 cooling systems with and without a hole drilled in the thermostat, it's pretty easy either way and I would not bother.

On the street I do not think you want to slow warmup or lower the lower setpoint in cold weather. If drilling the t-stat "fixes" something, you should instead fix the real problem. Cool running on the street can lead to major carbon buildup, stuck rings, etc.

On the track, I dunno, maybe there is a cooling gain (or reduced parasitic loss) from drilling it or you have a softer landing if the thermostat fails closed.