From what I have seen, any hop up chamber can be equal to another, it just depends how much work you want to do. I put a custom made nub in mine that helped a lot. The only reason I would do a PDI over the aero is that the PDI is made for the L96 barrel and the Aero is not.
As far as the spring goes it depends on both the compression and the barrel size. If I went to a 6.01 like yours then I'd probably be around 630 easy, just because of less tolerance. If you do enough reading on BBs and airsoft ballistics you will find that the generally accepted margin is about 0.08 tolerance between BB and barrel size, for spring guns; HPA/CO2 is a whole other world.
What are you chronoing right now? What custom work have you done to your cylinder? I would do all the mods and upgrades you want to do first, then replace the spring last. You can gain a lot of FPS by just making proper seals and tuning your cylinder and hop up for the proper spacing and sealing everything first. If I remember correctly my ASR was shooting about 450 out of the box, and if you have the Echo1 upgrade kit and the 6.01 barrel, it would not be a stretch to make it to 550 by just tuning your current set up and using the spring that you have.
Edit:
As an after-thought, you might want to consider why you want to go to ~550. There are some very effective sniper rifles on this forum that are only around 400-450. The only reason my ASR is as hot as it is, is because I only use that one for backyard games and the field that we normally play is large and everyone with an AEG shoots hot anyway. In normal games I use my G36 DMR (in the gallery) that only chronos around 430.
