The higher the stage, the more the shock does. The stage 5 is for racing. From what I've read on their website, they seem to recommend the stage 1 or stage 2 for the P1k, but you can get any stage that you want. It all depends on what you want to use it for and for how much $$$ you want to spend. The stage 5 shocks are pretty steep
I agree with you on only wanting to buy shocks once. I really don't think that you can go wrong with any of the Elka shocks. The guys from Dirt Trax TV said that the Elka shocks are the best on the market. I don't have any experience with them, or Walker Evans, or Fox, so I'm not an expert by any means.
I was looking at the Elka's today. I have a front shock leaking pretty bad. I'm sure Honda would cover it, but I don't like the OEs anyway. I'm debating between these and the Walker Evans.