Should I Postpone Graduate School?
Some opinions that may be helpful.  I assume this is in the US because as far as I know other countries do not use the Physics GRE.


The Physics GRE is a stupid test.
You seem to have what you need except for a good Physics GRE score.  (Assuming you attend a reputable school.)
Not all good programs require a GRE score.  Maybe you should apply to the the ones that do not.
There is no point in getting your PhD in a mediocre department.  Do what it takes to get into a good program.
Don't postpone a physics PhD for financial reasons.  Assuming you go to a good department, you will be reasonably paid while you are a student, and you will make a lot more money after you finish.  Loans may be deferred whine you are in school.
It should only take a few months to improve your Physics GRE score a lot.  


On the whole, I suggest a one year postponement.