First of all, unfortunately, there is no hard and fast rule to improving your score 100 points or so in any time frame. HOWEVER, the good news is that it is definitely possible!

There are a few questions for you, though:

1. Was your score of 620 on an actual GMAT exam (or a practice test)?
2. Did you get your score of 620 BEFORE you put in any good studying time, or was it after?
3. If you have already studied, was it entirely self-study, or did you take a prep class or get tutoring?

In addition to the study materials you have already listed, I'd also recommend getting the purple OG for verbal review. Remember, studying for the GMAT is all about QUALITY, not quantity. Really take the time to analyze each problem to see why the correct answer is the right choice. Don't worry about whether or not you can get through 100 problems a day, but rather try to get the most out of each problem you do work on.

Good luck!

You can take a look at powerscore CR bible. this should help you to improve on CR and RC sections. If not already done then read the answer explanation for each question in OG 11 and make note of every new point you come accross, revise these notes on regular basis.

thank you for the reply guys.. here are some clarifications.

620 was my actual GMAT score.

for practice i used the Manhattan CAT and i scored a 610 leading up to the exam 610 (40Q 32 V) so i knew where i was at.. at that point it was too late to reschedule the exam so i went in hoping for the best, although i knew i wasn't going to walk out with a miracle score of 700+ i knew i would be in the low 600 range.

It took quite a bit of preparation/ studying getting to this score.. only 8 months before I was scoring around the 480-490 range on the GMATPrep. I took that as a sign to sign on for a prep class. I chose Manhattan because the online schedule they offered matched the my working/studying schedule, and the online CATs were very appealing.

Thanks again for the input guys.. seriously your suggestions will not be taken lightly and I will try whatever it takes to get to a 700+ score.

Verbal can often be improved by working some Logical Reasoning problems from the LSAT. These problems tend to be more difficult and often provide better practice. Also, reading well written newspapers and periodicals can often improve the RC score.