Love your charts!
So here's the deal: you should be getting those really hard questions
wrong faster. Seriously! The test will ALWAYS give you questions that are too hard for you, because it will always just keep getting harder till it finds something that you can't answer. It does that to me, too. :) Your task is to recognize when the test has finally found your limit and LET THOSE GO! Then, you'll have enough time to spend on the questions that you really can answer later. (And, again, this happens to me too - they do find my limit!)
Re: your question about how you can sustain your score at that level: right now, you're not actually truly at that level. You're only really reaching that level
when you spend too much time. A true 99th percentile tester can answer those questions in 2 minutes (or faster)! So you're not actually performing at the 99th percentile - scoring level is a measure of
both accuracy and timing.
Could you learn to do so? Possibly. But it'll take a LOT of work. It's REALLY hard to perform at that level. And is that something you really need? There's no school out there that's going to reject you because you only hit, say, the 90th percentile.
And you're probably already between the 90th and 95th percentile right now, but you're underperforming because you're mismanaging your time. If you can learn to balance your time better, that'll boost your score right there. Then you can decide whether you want to expend the large amount of time and effort it would take to attempt to become a true 99th percentile tester. :)
Read this and start doing what it says:
http://www.manhattangmat.com/blog/index ... anagement/And I also highly recommend that you read the Scoring section of our free e-book The GMAT Uncovered Guide. You can find this in the downloads section of your MGMAT Student Center.