Magento should be much more powerful (in principle) than he's depicted in X-Men. He controls the EM force which is the strongest long-range force of nature. The strong force is 100 stronger but only acts at subatomic distances.
Magneto should be invulnerable (except to the strong force) and be able to produce extensive blasts of energy.
Galactus should be equally powerful (if not thousands of times more), though i don't know exactly how his powers work. In Sci Fi energy does not have a real meaning therefore Galactus' power should be near infinite because Galactus can absorb all the energy of the cosmos.