You will never see one with more than 4 questions on the exam - gmac simply published more than 4 in the practice sets.

As or timing, 2.5 mins for shorter passages and 3.5 for longer passages

The questions published in the Official Guide represent a range of questions available for the passage. You see, the computer selects the passage and the 3 or 4 questions for that passage all at once and it does not adapt based on your performance. So if you miss the first 3 you will get the same 4th question as you would if you got the first three right.

The questions themselves are an element of the difficulty and you will find that the official Guide questions often ask the same thing in two different questions - except that one of the questions is more difficult than the other.

I like what Brent has to say on timing - a little extra time spent really understanding/ analyzing a passage can make the questions go quickly!