Depending on shock, I might need as much as 700!
Also, I have a Trunion mount rear shock, so I'm not sure if I can even get a better shock of either type.
I think it is a matter of changing the shock mount kit to a Trunnion fitting on either an Air or Coil shock.
I saw this on a Trek analogue frame so I presume it might be the same on your Powerfly?