You guys don't seem to understand Magneto's powers. They aren't internally generated for the most part.
They're more akin to Storm's in that he can tap into and shape the energies around him as she basically does when she manipulates the weather.
That's how Magneto was able to literally yank the bullet containing Kitty back to earth from where it was in space.
So yeah, I'ld say Magneto's a match for Nova.
The actual fight between the two would be along the lines of a bull fighter vs a bull.