From what I've seen, there are many more differences between the two fields than similarities. However, to be honest, I don't have that much experience with PM&R. My only real interaction with them has been during neuro rotations, specifically, when managing stoke, spinal cord injury and traumatic brain injury. Regarding management, neurologists usually manage the actual injuries and physiatrists manage the rehab from the injuries. It's true that neurologists don't do many proceedures (mainly LPs and nerve biopsies), unless they do interventional pain mgmt (pretty uncommon). Also, regarding EMGs and NCS, it's my understanding (correct me if I'm wrong) that most initial diagnostic studies are done by the neurologist and progress studies are done by the physiatrist. Neurologists also do EEGs and diagnose and/or treat diseases of the CNS and peripheral nervous system (dementias, epilepsy, peripheral neuropathies, pain, stroke, infections(encephalitis/meningitis), non-surgical trauma (spinal cord and traumatic brain injury), MS, headache, cancer, Parkinsons disease, Huntingtons disease, muscular dystrophy etc., etc.)
Like drusso said, it all depends on what your interests are. If you like rehab, sports med, occ med, interventional med etc., go PM&R. If you like neuro, then go that route. I think both fields can be quite profitable...it mainly depends on how many procedures and electrodiagnostic studies you do. I know several neurologists who do quite well.