We used to say to judge based on the passage length. For a shorter passage (fewer than 40 lines in the OG), you'd give yourself 6 minutes to read and do 3 q's, and for a longer passage you'd take 8 minutes to read and do 4 q's. We no longer give this specific advice, because the GMAT doesn't necessarily hold to that pattern, and as Rich said, your reading time will naturally vary depending on the content. However, these can serve as good *rough* guidelines. It's certainly a good idea not to do all the questions in one timed set, because you'll never see 6 q's on the real test. By the time you get to question 6, you'll be an expert on the passage and your performance will be unrealistically high.
Here's what I recommend:
*Start by doing a few passages for which you simply note the elapsed time for each element. How long does it take you to read and analyze the passage? How long does each question take?
*Keeping in mind your current performance as well as the general guideline of 2 min/q (including reading time), start doing timed sets in which you hold yourself to a set amount of time to read the passage and answer 3-4 q's.
*You can do the rest of the q's under separate time or set them aside in case you want to revisit the passage later with new questions. The main thing is not to use them to gauge your accuracy. For instance, if you get 4/7 correct but it's the last 4, that would mean 0-1 correct on the test!
Also, it sounds like you're going for high-volume practice, e.g. doing a bunch of problems or passages in a row. You're much better off doing one passage at a time and really learning from it before moving on. If you're reviewing correctly, the review process should take significantly longer than the original timed experience, and that's before you even check your answers. Ideally, you should be able to explain the following:
1) The author's point and how each part of the passage relates to that point.
2) The meaning of each question and (if possible) the prephrased answer (i.e. What answer should we expect before looking at the answer choices?). What material in the text supports that answer?
3) Why each answer choice is right or wrong. Be as specific as possible.
4) If you catch any mistakes on your part, what led you to those mistakes? How might you have avoided them?