Well, I cannot speak from experience on this one. You are head and shoulders above me on this one - I am still struggling with the fundamentals.
However, I wanted to say one thing. I have been scouring the "Beat the GMAT" forums, and I have noticed that many were having this problem on practice tests. One guy was only getting a consistent 640 and 650. On test day, he got a 710!!!!
I think the moral of the story is that these tests are just measurements of the actual test. You never know.
I hope to perform as well as you do. You are doing great!