I was surprised at how hot steppers run - problem is that they need to draw power even when stationary to hold position. As said above, most stepper drivers have a "half-current" option that reduces current to half when the motor is stationary for more than a second or so, which reduces heating considerably. I aim to have my motors run at about "just not quite too hot to hold", which is around 60C.

I start with the nominal rated current of the motor, based on its spec, and set the driver accordingly. I then adjust the max current so that in normal use the motor ends up at about the temperature as mentioned. There's a lot of discussion around things like peak/average/RMS current and what the driver settings mean. These discussions usually end up with a general conclusion of "search me, Guv!" as no-one is quite sure what the driver and the motor manufacturers are specifying. Hence the rule of thumb, "adjust so it's at about the right temperature."