The docs I know who work in preventative medicine are internists that are board certified in infectious disease and have MPH degrees. They travel a lot and give many presentations. I can't comment about the stress level, but they all seem to love what they're doing. Obviously, you must enjoy traveling and giving presentations.
Preventive medicine is a broad field, with many opportunities for career growth. You can work in epidemiology, health services, administration, academia, research, etc, although this type of work would not involve direct patient care. Here's a list of jobs for MPH degree holders (some jobs are for people with MD/DO or PhD degrees): http://cfusion.sph.emory.edu/PHEC/phec.cfm