It sounds like you have an in-depth finance and accounting background which will bring a lot to a b-school application and program, and increasing your GMAT to the level you hope for would certainly help your chances at the competitive schools you have mentioned. Stanford is a reach and very competitive to get into--not only are they very selective with some of the top applicant stats, they also have a smaller program than, say Harvard, so the % who are accepted is very small. The others will still be challenging but your odds are greater for acceptance, and in general the decision will be based upon how well you make the case in your essays that you need an MBA, that you have clear short and long-term post MBA goals, that their school's specific program is best for you for specific reasons, and that the MBA will add enough to your career path beyond the MAcc you have to make it worthwhile.
Wishing you the best in the application process!
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