You really need at least 680 at a bare minimum - and realistically 700+ to be competitive at the top schools. Even with a 700+, you'd be a stretch for certain schools (Stanford) and a slight stretch to sweet spot (depending on the quality of your applications) at the other schools.
Re-take the GMAT. Do what it takes to boost that score. And if you can't, then apply anyways, but know that your GMAT is going to be a significant handicap. I wish I could tell you otherwise, but that's just the reality.
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