6 weeks from now, I understand that its first week of May. Unless you are applying in European Business schools or planning to consider R1 for Jan'18 intake, there is no need to hurry or consider the 6 weeks time frame.
Moving on, I suggest to slow down, since 6 weeks is too less since you already took the test twice with no such score increase. So, better consider 9-10 weeks, review the Manhattan guides, along with kaplan premiere if possible, redo all the OG problems, and you are ready to hit mid 600's, your target score. Alternatively, since you already have access to EmpowerGmat, you can complete the full course, and then shift to OG problems. Whatever you do, accommodate the OG problems in your schedule. You may consider taking two CAT through out the process - one in the middle and one at the end.
Good luck !!