it seems you've already identified one of your main flaws - spending 6-7 mins on any question, no matter what the difficulty, is killer. it takes away valuable time from other questions, and you'll be forced to play "catch up" the entire test.
knowledge isn't everything on the gmat. in fact i'd venture to say (this is my opinion) that it's not even the most important thing tested! the most important aspect is timing (and along with that, knowing when to quit on a question).
to give you an example, during my gmat there were several instances when i knew i would have no shot on a math question. this wasn't because i didnt know the formulas or the fundamental knowledge, but rather it was too cumbersome to sit down and tackle, and would slow my pacing down. in these instances (not many - maybe twice or 3 times max) i opted to skip the question altogether and just guess - rather than taking 6 mins to solve it.
i know it's tough to do (especially if it's a seemingly easy question) , but if a question is taking you longer than 2-3 mins to do, then cut it as a loss, make an educated guess, and move on to the next one. and don''t ever ever ever leave a question blank on the real test - that's killer too.
the real trick is knowing WHEN to quit on a question. please don't interpret this post as meaning you should skip any question that seems difficult. this is something you get by taking multiple full length tests. i'd recommend to spend the last week trying to focus on mastering this skill.
to give you some hope, the
mgmat tests are generally thought to be a little harder than the actual test. in fact on my
MGMAT tests, i scored between a 660 and a 720. so you definitely have a realistic shot of achieving your goal