Nice work on the 700!
As far as I can tell, the GMAT is extremely consistent about giving you four RC passages per test, despite the occasional report of something strange happening on an exam. Sure, you might see more RC passages toward the end of the test, but GMAC definitely isn't on a campaign to bombard you with extra RCs at the end of a test, regardless of your score. The best way to handle this in practice is just to keep track of the number of RC passages you've seen. If you get to question 30 and you've only seen two of them, odds are good that you'll have two more coming at you.
The difficulty level of the passages is mostly determined by your performance up to that point in the verbal section, and if you did well on the first 30 questions, it's likely that they'll hit you with some relatively tough passages. But keep in mind that it's awfully hard for a test-taker to accurately perceive the difficulty level of RC passages -- to a large degree, the difficulty level of GMAT RC questions is in the eye of the beholder. If you love reading about science but struggle through passages about, say, the arts or humanities, you might feel that a particular set of passages about literature is unusually tough; somebody else might have exactly the opposite reaction to the same set of passages. So this isn't comforting, but sometimes it boils down to luck: if you happen to get passages that you find appealing, comfortable, or interesting, you'll think that they're easier than they really are.
But don't worry about any GMAT conspiracies to torment you with unusually difficult RC passages at the end of tests. It might feel that GMATPrep #2 was out to get you today, but the algorithm hasn't fundamentally changed into an evil beast that is targeting you personally with extra RC. (Though perhaps the GMAT algorithm is, in general, kind of evil… but that's another topic entirely.

) It sounds like what you saw today was probably within the normal parameters of the test.
You're already at a 700, so just keep up the hard work, and you'll be fine!