I think it would be easier to follow your PFTs if you are really looking to "classify" your severeness. My Doctors have always stressed the importance of doing my meds and treatments as prescribed, whether I feel like I need it or not. It was explained to me that treatments are done proactively, I should always do airway clearance, (even if I wake up feeling like I don't need to cough anything up) because there may in fact be mucus that needs to be moved around and worked out. And since our mucus is a breeding ground for bacteria that other people's lungs are not suseptible to, we should be working it out of there. And, in my experience, getting into the habit of doing treatments (whether you feel like you need to or not) will make it just another part of your day...like brushing your teeth. I think this routine is especially helpful for those rebellious pre-teen years, when CF can be hard to deal with, and you may not feel like doing yout meds!
I have what I guess is considered "normal" lung function (in the 80s), and was often above 100 in my younger years. However, I ALWAYS did my treatments, and I don't consider myself "clinically dependent". I lead a very normal life, I just have to do the vest and other meds that people with CF don't have to do! <img src="i/expressions/face-icon-small-smile.gif" border="0">