It was difficult for me to assess whether I'm ready for the GMAT. Much less for me to assess whether another person is ready for the challenge.

However, I like to contribute my experience:
1. It is difficult to assess your final score based on the prep test. My prep test scores didn't closely co-related to my eventual GMAT score. Maybe it is because I only took about 5 or 6 prep tests - 2 powerprep, and the rest are from Kaplan. The PP scores were always on the high side (maybe because of the OG) and the Kaplan scores always on the low side (I honestly feel the Kaplan tests are not very well developed). I think my actual score is about the average of the 2 PP tests, with a variance of about 30 points.

Having said that, I always encourage test takers to go for the full-test prep, as it helps to condition our concentration for the 4 hours test. Use these prep tests to "get a feel" of the actual test - save your US$200.

2. During the actual test, I thought I screwed it. The Quant questions seem to be mainly on the easy side. And I had only a few minutes for the last few Verbal questions (I was hit with a RC quite late into the test, if I remember) - had to guess for the last 2 or 3 questions. I thought I would only get about 620+/-. Was thinking of whether I should cancel the test. At the last moment I thought I would just accept it (thankfully). I got 700+.

Bottomline: I guess many people will feel that they didn't do well, immediately just after the test. However, it is really unpredictable. Personally, I feel that unless you did not manage to complete the sections, or had to guess thru the last 10 questions, it will be better to accept the results.

To answer you question on whether you should wait for one more month: Your prep sounds amazing. I think an additional month of prep may only be marginal for you. Futhermore, you may run a risk of burnout (especially with your 10 challenges plan). In economics, they call it Law of Diminishing Marginal Returns.

Anyway, you need to book for the test early. It is not like you can book to take the test tommorrow if today you feel that you are ready. There could be a few weeks of waiting time.

Well yb, I agree with coffeeloverfreak,
Write the test whenever you feel armed & confident. Just think, whether you can do it now or need some more time!

I'm not really a veteran - I only took my GMAT once

As you can see in my posts, I'm not too concerned about the test scores. As mentioned, I scored quite low for Kaplan tests. About 2 or 3 weeks before the actual test, I only managed a mid-500. Had I used that as a guage for my readiness, I would not have taken the actual test.

However, I feel that one must be able to last thru the entire 4 hours during the last few prep tests. This is more important than the prep-test scores.

See an interesting post: http://www.gmatclub.com/phpbb/viewtopic.php?t=21885

If you really want to use prep scores, many people say look at the powerprep. However, the score may be biased because of the OG.

All the best!

Agree with Hjort about it being more a state of mind than a number. When you're feeling like you truly understand the problems you're reviewing, and you can attack them quickly and really understand why your answer is right or wrong, then you're probably ready.

A nice confidence boost is to write the second PowerPrep test a few days before you write the real thing, as the last CAT. The score should be inflated because you'll have gone through the OG by then, and PP scores are higher than other practice tests like Kaplan.