I'm very confused! (SAT® problem)

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Well, the problem is this: yesterday I opened this Barron's book for the old Writing 2 to read some sample essays because the essay hasn't changed for the new SAT 1. And there were samples for essays on the same topic with marks from 6 to 1. Ok... BUT I just couldn't find why one essay got 5 and another got 6. The explanation below was unclear and, honestly, I don't quite agree with it.

Anyways, my question is about the essays. Could someone recomend me a good book with VERY clear essay samples and explanations. I think I'm good at writing (not that much of a catastrophy like a couple of months ago) but these SAT essays are very unclear about their requirements.

In addition, I'd like to ask something else. To prepare for the Critical Reading should I read books like "The Great Getsby" (оr whatever other you could recommend. Only one really hard I've read is "The Lord of the Rings") where I can find the "harder" and more literature specific vocabulary? I did well on the TOEFL Reading but I believe the SAT narratives will be harder than the VERY BORING history lectures in the TOEFL.

I'm very sorry for the long post but I thought I'd better ask everything in the same place rather than make two topics.