Correct Tyle, the wattage rating for a fixture is really for
protecting the fixture and the wiring from overheating.

I've done a lot of fixture replacements in my life and you can always
tell when someone has been burning too high a wattage bulb in the
fixture because the wires in the ceiling box have insulation that
cracks and falls off. That's why the base of the fixture has
insulation. It's not really for keeping heat or cold from coming in
but to keep the wires in the electrical box from baking.

If you have a lampholder that is porcelain, that's much better then
the cheap paper lined brass lampholders.