Is graduating early from college or transferring to another college fine if I took all the upper level courses? I'm currently a sophomore at a small liberal arts college. I want to get into one of physics PhD programs with faculties renowned for quantum gravity. I'm majoring in math and physics, and since both departments in my college are small, I will have taken all the upper-level courses in math and physics until the next semester. My major GPA in physics is 4.0, and my GRE physics score is 990, but I will have no math or physics course to take after the next semester. There aren't much research opportunities here. The only research opportunity is available during summer (which is experimental physics, but I'm mainly interested in hep-th). All REUs are not available for international students. (However, there are a few programs available for int'l students, such as Caltech SURF.)

Which of the following choices would be the best?


Graduating early (3 yrs), going to physics PhD program, and saving $>60k. If I don't get into programs of my choice, I will either stay in the college, in the program until the end, or (hopefully) transferring to them after getting non-terminal Master's degree if I will have a compelling reason.   
Transferring to a high ranked research university for advanced/grad-level physics courses and for more research opportunities
Staying for 4 yrs in the current institution
Only in exceptional situations should an undergraduate consider "getting out early" from their undergraduate education to pursue graduate study.  Your situation is rather exceptional and is one of the better cases for doing this that I have seen.

My honest assessment is that you sound like an outstanding student who didn't make the best choice of undergraduate institution.  Liberal arts colleges can be great for a wide range of clientele, but someone who maxed out the subject exam in their intended field of graduate study in their freshman year is probably not in that range.  If you know you want to go to graduate school in physics, you want to be taking physics courses over the next three years: independent study is okay, but it is probably not good enough.

I recommend that you apply both to PhD programs in physics and to undergraduate programs at top tier research universities.  For the latter, you are looking for more than just being able to transfer in: you want substantial scholarship opportunities (I would aim for a "full ride") and specific access to faculty and their research.  

It is of course likely that you will get admitted to better undergraduate programs than PhD programs.  In my opinion if you get into an absolutely top undergraduate program with a substantial scholarship, then that's the way to go. Most of the students who are at the very top PhD programs started out their undergraduate career with a roughly similar trajectory to yours and then built on that substantially through four years of a superb undergraduate program.  I  would be a bit surprised if you got admitted to one of the top ten programs without an undergraduate degree.

If I may throw out one specific option: the college at the University of Chicago is a lovely opportunity to get a liberal arts education in the midst of an absolutely world class research university.  You can read Plato and Kant and Dostoevsky while taking graduate courses to your heart's content.  Moreover they have full ride scholarships available for exceptional students.  (I went to the University of Chicago on a full ride scholarship, read all of the above authors, took many graduate courses in my subject of interest -- mathematics -- and then got into all the graduate programs to which I applied, including the top three.  I am more satisfied with my education at the UofC and my decision to go there than almost anything else in my life.  Seriously.)