First off, your 680 is a great start! You may want to check out this write up of our student Abhay's prep experience. He scored a 770 after finishing his Knewton course:http://www.knewton.com/blog/knewton/inside-knewton/2011/02/21/student-spotlight-abhay-prasanna
If you go with Knewton, you'll also benefit from our 50-point money-back guarantee. With 680 as a baseline, you'd assure yourself of scoring at least a 730. By making use of our Verbal strategy lessons to achieve a better Quant / Verbal balance, many students end up scoring even higher.
Hope that helps, and let us know if you have any questions!
I was sure of going ahead with Knewton , but there are two things that confused me after reading the reviews
1. Majority of questions , as per the reviews , falls into Easy - Medium range , which i am not sure will help me since my base score is already 680. Maybe that is the perspective of the people who wrote the reviews rather than the actual thing.
Could you please suggest
2.What the reviews says that questions are minor alterations of the Official Guide . So , can i expect variety of practice in Verbal section of the course , once i enroll ?