I use 650F for soldering on printed circuits, and I kick it up to 700F for wiring if it's heavier and slow going at 650F. It's worked for me for a lot of years, and I get a lot of mileage out of my soldering irons.
For track and stuff like #12 wiring, I break out the Weller 100/140W gun, I'm sure it gets a lot hotter, never measured it.