I can tell you from personal experience that a 5.2 is to soft. For '01 and '02, RT's rate recommendations were a little soft for the YZ's. But I had to learn this through trial and error. I might hesitate in going to a 5.6, though I bet it would fall within sag specs. If your local RT guy is willing, I'd try a 5.4 first, and if sag/free sag measurements are in the ball park, run it and see how it feels. sometimes i can get 2 different springs to fall within the appropriate ranges (obviously one will be towrd the softer end and vise versa) and then its all a matter of personal taste. Though I'm fairly aggressive, I like to run a softer spring. But thats me. some people like the firmer feel of the stiffer one.
Most tuners agree that there should be some free sag, so you don't top out the shock needlessly. The standard should be no less than 1/2" free sag. However, maximum free sag should be approx 1". Not everyone agrees on this number though. some say it can be as much as 1 1/2". I personally don't have a problem with this number, though my "magic" free sag number is 3/4'', though it usually ends up right about 1".
If you do have more than 1 1/2", you should look at a softer spring.