To be honest, my opinion is that if you try and adhere to a set of guidelines based on the temperature, you're just going to lull yourself into a false sense of security. The reality is, most of the guys on the forum have more than enough horsepower to destroy their cars whether it's 90 degrees or 9 degrees. And if you're doing something that will wreck your car at 55, it probably will at 65 or 70. My suggestion would just be, if you think it might be a bad idea to go hammer down, that means it is. No matter what you do, you can't change the temperature of the surface you're driving on. My other suggestion would be to remind yourself every time you get in the seat that the GT is capable of more as a car than you are as a driver. The GT doesn't forgive once you cross the point of no return and as we all know at this point, it gets easier and easier to do that the colder it gets.
This video was from November 3rd, 2006. I drove the GT 130 miles to the dragstrip (with occasional flurries) and it's the one and only pass I've ever made. I was very concerned about leaving hard because of the low temperature so I rolled out easy and ran 11.62@132.9 mph on the stock F1s. I checked the historical weather data and the low temperature on that day was 24*, the high was 37*, and when I made the pass later in the day it was probably ~30*. I'm pretty sure I'm the only person that's ever run a GT at the track in the low 30's (or maybe even high 20's).
[video=youtube;EKrp63e7KGc]http://www.youtube.com/watch?v=EKrp63e7KGc[/video]