Hi. Congratulations on your career!
I would strongly recommend against taking a break from work especially if your career is progressing.
It is an extreme idea to quit work to prepare for the gmat. Most people are able to reconfigure their days to study for the test.
Very often, you only have two a maximum three very productive hours per day to study and so quitting your work to only gain two or three hours per day seems to be an overkill.
Quitting the job has many problems including weakening your position as an applicant, weakening your position as a job seeker both after MBA and should the test not work out for you. So it’s a not only a risk but also a move that will not have a win, even if you get a super high GMAT score you will still shoot yourself in the foot because you’ll have a gap on your résumé and issues finding recommendations and so on.
Perhaps a better option if you feel like you absolutely must take a break and your job is super demanding is to take a leave for a month so it doesn’t show up on your resume or switch jobs and work in a month of a break. You don’t need six months to prepare for the gmat. It’s actually kind of productive to take that long, all you need is three months of a couple hours per day but those must be very productive hours perhaps early morning before you go to work.