gp04cluster.jpg
Using Torque, these are my best approximations for temp gauge positions on the 2004+. With the cold line at 140, the line increments are about 9 Farenheit. Most other GM uses 210 as a center line, I assume this is the intent with Pontiac, and I assume that all other GM is 212 at the 210 line. I read somewhere (cant remember where) that GM's with gauges that go to 260 are actually 265.
Under normal conditions, crusing with the AC on, my gauge will be a little above the 194 line, a little below if not using AC or its very cold out. At idle, it will reach the 221 line where the fans kick in and drop it back to the 203 line (assuming the shut off point is 200?)
This is the highest my car has been under my ownership, my water pump failed and I pulled into a Wendys when I noticed the coolant smell and the steam.
Keep in mind that these gauges are not meant to be dead on accurate to the degree, the PCM reports on a several second delay. For example, my gauge has been on the 194 line when torque reads anywhere from 192 to 197. This just gives you an idea to within 5* +/-