Fair warning, it'* generally considered bad etiquette to post in a very old thread. Local staff can get quite excitable over it as well, and it'* even forbidden in forum rules if memory serves me well.
In reference to your question however, the general idea is to try and reduce or put off heatsoak in the supercharged application as long as possible, especially when running hard. Heatsoak tends to invite preignition, which can be very bad with forced induction. Stock fan settings will not allow you to capitalize on a lower temp thermostat usually, because the fans still allow the engine to run warmer before they come on. Fan overrides, or custom programming is usually necessary to use it to the fullest. Naturally aspirated applications haven't reported any gains from a lower temperature thermostat, and tend to be happier when running warmer for better combustion.
I ran a 180* thermostat in my Park Avenue for years and saw no benefit. The only difference you will notice will be that the temperature gauge may ride a bit lower while on the road or with the A/C running.
The hole is for bleeding air out of the system, because air will get trapped behind the thermostat, and can be a major pain to get bled out without the hole.