Hi. Sorry. That's a tough trade to make - which child do you love more and which one will get the life preserver?
Now, I know very little about your situation so take my advice with a grain of salt but I am familiar with your dilemma. Let me throw this out and you decide if you like it or not:
1. A bit shortsighted of you to schedule it for the 9th since Sept has 30 days, if you retake, you can only do it on the 10th of Oct, one day late for the applications (but I would not reschedule it for the 8th of Sept). Ideally you want to schedule your test 32-33 days before the deadline if you have to do it that tight so you can retake within the window since schools will take the scores that are even 1 day old.
2. If you postpone your GMAT, I would venture to say that you will NOT have enough time for the essays and the applications. I would not even waste the application fee for the Oct 9th, so you really don't have a choice (even though you think you do). ON the other hand, You have been through this - you may be a much better writer than I am and you had applied last year, so perhaps you can recycle some of the essays. I know I could not, so I would need a month (like you have wisely allocated).
3. I have no idea how much prep you have done but usually if you are retaking and at the end of it, 14 days will not give you more than 20 points at the end of the prep and even that is optimistic.
My suggestion would be - work your ass off for the next 10 days. Kill the GMAT and leave yourself a month for the applications. If you do not get the score you need, then schedule again for 31 days later and do not apply on the 9th.
My 2 pesos.