If you want an idea of how hard it is to get a job in academia as a physicist, all you need to do is compare the number of matriculating grad students to the number of new faculty each year. Here at Davis, the first number is around 30, and the second number is a bit less than 1. Assuming these numbers are representative, you should expect at most a 1 in 30 chance of getting a faculty position. I've heard that at top 5 schools that number is more like 1 in 10, but the order of magnitude should be right.
That number gets worse the more abstract the work; most faculty hires are in condensed matter experiment, then probably astronomy/particle experiment, then various phenomenology/computational faculty, and lastly theory. In contrast, a bit under half of the grad students here work in fundamental theory or some sort of computation; for these students, the naive likelihood of getting a job hire must average out to something like 1 in 100*. But probably what you should get out of this is that if your motivator in grad school is an eventual faculty job at an R1 university, that's a lot of eggs to put in one basket. If your motivator is ''I'm going to do something I love for the next 6 years,'' then the 1 in 100 number shouldn't matter--you should do the thing you love.