I got one of those dip-stick oil temp guages and since there's no red line or anything I was wondering at what point do I get concerned.

It would be nice to know at what temp will oil begin to fail. And will using synthetic raise the limit?

 

The general rule is 250 Degrees F for Dino oil, and 300 degrees F synthetic. Remember you have to add 15% to the Oil temp taken at the tank. That will give you a good idea of the Cylinder / Head oil temp.

 

Unless it's old Iron I wouldn't worry about it.
My 95" TC has seen all day rides where it never dipped below 100 degs and much of the day was 115 to 120 degs.
I don't even have an oil cooler but she runs through the heat fine.
105,000 with 65,000 miles on the 95" kit.