Hello sdas, thanks for your question.
I have to admit, I do not specialize in career advice, but I will offer my opinion.
You’ve mentioned the GMAT, but not once business school or your future career path should you take the test. To me, this seems like a broad, abstract goal of yours. On the other hand, it seems like you are excited about this new opportunity, which is real and specific. It seems like your hard work has paid off.
Because you frame the options as a promotion at another company that you’re excited about versus just taking the GMAT (which is just a test, I have no idea what you would do with the GMAT), it seems like you might pursue the opportunity and take the GMAT later on in your career, should you ever see a specific need to.
Just my two cents. Hope it’s helpful!
Best of luck,
Brian