Hi dilip_dx,
The scoring algorithm on the Official GMAT is far more complicated than most people realize. Since that algorithm is proprietary, no GMAT company has an exact match for it, thus CAT scores can vary a bit based on the 'biases' involved in their respective designs. The most realistic CATs available are the 6 from GMAC (the 2 free CATs, and each of the 2 that come with Exam Pack 1 and Exam Pack 2), but since you have not taken any of those CATs yet, we do not have a definitive sense of your current 'ability level' yet. There's a significant difference between raising a 640 to a 700+ and raising a 680 to a 700+. As such, I suggest that you take one of those Official CATs sometime soon (perhaps this weekend) - and do so in a realistic fashion (re: take the FULL CAT - with the Essay and IR sections, take it away from your home, at the same time of day as when you'll take the Official GMAT, etc.). Once you have that Score, you should post back and here and we can discuss the results.
Assuming that your current Quant skills would place you around a Q50, then most of the missing points that you are after are going to be found in the Verbal section - and thus, you should be spending more of your time honing your Verbal skills than honing your Quant skills.
1) What study materials have you used so far?
2) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich