The U. Cambridge (S. Hawking and N. Turok territory!) Tripos cirriculum says this in their description:
"Differential Geometry applied to Physics, with applications to Maxwell Theory, General Relativity, Quantum Mechanics and parts of Quantum Field Theory, String Theory and M. Theory"
I also notice most of the applicable physics course descriptions do NOT specify DiffGeom as a necessary prerequisite, but promise to develop what is needed in the body of those courses. They probably want to emphasize that the physics preparation be adequate.
You might think more along lines of what physics tools-of-the-trade are needed. Mathematical techniques are apt to be an eclectic grab-bag.
link ->
http://www.maths.cam.ac.uk/CASM/courses/descriptions/
U. Camb. Certificate of Advanced Study in Mathematics