Last weekend I took my car to trackday, and drove really badly..
First time out, and I overdrove the car so bad it was embarassing. Most corners entered way too fast, and alot of sliding. I have awd, so there wasn't alot of drifting as such, but alot of sliding around and locking up tires.
After a few laps I noticed my tire grip degrading noticeably, especially in the last corner which is a sharp hairpin where you whip the car around. The pit entry is on the outside of this corner, and the pit exit itself is around 20m onto a staging area. On one of my runs where the tires were really bad I exited onto this staging area and immediately felt the tire temps with my hand, expecting to burn my hand. To my surprise the tires felt definetly hot, but not burning hot. I would estimate around 50deg C. This is performance street tires. With the amount of degradation to grip I was expecting REALLY hot tires. I can't imagine what it would be like driving on tires 150 or even 100degrees, but I assume it would feel pretty greasy.
Now, it COULD be that my tires just cooled down really fast, but I was off the pace for a maximum of 15-20 seconds before the car was stopped and I was out and touching the rubber. I felt the tires after about a minute and they still felt pretty hot.
Now I know this is in no way scientific, but a subjective observation, but still I think I can tell a difference between 50 and 150 degrees.