Agreed with purplebutterfly! GW is approx. $1200 per credit hour, so transfer whatever credits you can, especially if you think you have a good grasp of the material. You should transfer statistics and possibly research methods, because the course material does not change throughout various programs. For courses that are a little more theoretical, I would take them, because most likely it will be helpful for comprehensive exams.
Transfer credit not necessarily saves you money, because there are some stipulations with financial aid. If you are going to take a loan, you will need to stay a full-time student, therefore above a minimum amount of credits- THIS IS VERY IMPORTANT. You do not want your loan payments to kick in when you are not able to pay for them.
The good thing about transferring credits is you will be able to take an extra class here and there to either lighten up your load, or just get some elective classes that might of be of more interest to you. I plan on getting all my required courses out of the way and then take courses in the Washington DC Consortium. You also must remember that transfer credits are on a case by case basis and must be approved by the professor, your advisor, the program director, and Dean.
The maximum you will be able to transfer is 27 credits at GW, but most likely you will not be able to transfer that many. Even if you are able to transfer a semester worth of credits, you will still have your dissertation/Major Area paper to work on and externship, so graduating early is not really possible. Internships do not accept applications until the Fall, so even if you finished your course work early, you will be waiting.