To know how high of a GMAT score is like asking to know what the lottery numbers are going to be. There are simply way too many variables in the application (22 or so variables) that will, can, and may play a role in your final decision. To name a few, certainly GMAT and GPA play a crucial role. But what's also important is your work experience, the quality of work, the name of your work, the responsibilities you've gained and the actionable items you've achieved, the extracurricular activities that you've shown, led, and initiated, the essays that you're going to write to discuss your goals and other subjects, your letter of recommendations....
With all that said, it's hard to say what will counter a 2.5 GPA. My suggestion to you is that if your dream is to achieve a certain rank of school (such as UCLA Anderson range [I consider Haas to be a bit higher in ranking]), look at the averages and see where your statistics lie. And of course, at the end of the day, your chances of admission if you don't apply is zero. So I would still apply if it's your dream. To answer your question with EVERYTHING in mind, a 720+ on GMAT would be a good target for Haas, Anderson, and perhaps even Marshall.
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