I did a lot of reading in the different GMAT forums before I signed up for my Princeton Review online class, and I never got the impression that you would limit yourself to a 500-600 score if you took PR, or Kaplan for that matter. My practice scores are well over that, and I have gotten a lot out of my course.

Some of the other companies market themselves as elite prep for high scorers, but plenty of people get 700+ with PR or Kaplan, either with a course or by using their books. In the end, it's up to you to make the score happen. Choosing an "elite" prep option won't guarantee you anything. You have to work just as hard in one of those courses as you do with the others. My class has a LOT of work, and if I'm diligent about it, I'll do fine.

If you want to be really confident in your decision, what you really should do is go to the library and check out the different companies' books...see if you like their approach. Read through their strategies a bit, do some practice questions. You will see which method you prefer. I strongly preferred PR over Kaplan (tests are a lot more like the real ones), and I've been happy so far with my decision.

But I was very familiar with both before deciding, and if you do that as well, you won't worry as much about the subjective stuff you see in the forums. Even if you don't get a chance to do that, I really wouldn't worry. PR isn't going to hurt your prep efforts at all, and should actually help a lot.

Hope this helps!