Bond, my advice is retaking the GMAT. We all know about the GMAT and how you can get into HBS with a 580, it just greatly increases your chances as your score goes higher. You aren't a walk on water candidate, but your candidacy is strong given your WE and entrepeurship abilities.
To be honest, your candidacy is a far more interesting story than mine. I feel like the game really would work in your advantage if you could somehow manage the 700+ range, and the schools would be lining up for you and itd be your turn to pick from them.
In all honesty, If I stuck with 670 on my gmat rather than retaking, my firm belief is that I wouldnt have gotten 1 interview, let alone acceptance. Another thought is that you might be from an overrepresented group. If you are, it is probably much tougher to get in with a low 80% range GMAT. Its unfortunate that it works the way it does in my eyes, cause knowing your posts on here, I am sure you put together very thoughtful apps and worked hard to get in. Best of luck if you do retake.
If you really dont want to wait another year though, Darden and retaking simulataneously is a good way to go. If you are willing to wait a year snd get the GMAT up, you could be looking at an "M7" school. Not sure what that means, but a top notch program. Best of luck!