things you could change to make your pm lighter
Barrel
Frame
trigger
asa
reg
Basically anything you have on there thats stock weigh it up against and aftermarket product, if the aftermarket one is lighter then its going to make a difference.
When you've got the lightest of everything not much else you can do.
I believe if your after a major difference i'd start with a STAKO air set-up
Altho that aint gonna come cheap
Hope that helps...
Your more than welcome to try my ultralited pm5 at the next forum battle before you slosh out on £150 notes for one