There is really no such thing as a typical improvement. It depends too much on how you are studying, what your strengths and weaknesses are, and how you handle the pressure of the actual exam. Some people continue to score in the same range for months on end. Others do well on the practice tests and then fall short on the real exam. Occasionally, someone does surprisingly well (e.g. 50 points higher than their best practice exam). Generally, you should expect to score within 30-50 points of the practice tests you take within the 2 weeks running up to the exam. How much you improve between now and then depends on you. If there are still some areas where you can make quick progress, a 700 is still feasible, but if you have already improved a great deal up to this point, your real score may still be in the mid-600s.
If you want more specific feedback, post some details about your performance, or PM me you Manhattan info (name &/or email) so I can take a look at your CATs.