Do you mean the LED and the 20mm board are separate items, or are you talking about soldering the leads/wires from the driver to an already mounted LED?
If they're separate items, I have no idea about the temp. If you just want to solder the leads to an LED that's already mounted on a board, as long as you get the solder pads hot enough for the solder to flow onto the leads/pads you should have no problem.
My soldering iron gets up to about 900* (no temp control) and I've never had a problem. The finished solder joints should look kinda shiny. Make sure that the solder joints don't stick up too high. The driver could short out if the joints touch the bottom of a aluminum reflector. Been there, done that. :)
I usually use these > SKU 1138102
to prevent shorts. They may be a little hard to see, but they're there. lol
Edited on 11/24/2016 at 3:46 PM. Reason:
I just need one more flashlight. Just one. Honestly. :D