You could order the Crosman 4B mainspring (33 coils, .118" wire) so you have a spare but it won't give you much more power over the OEM spring, if any.
You could fill the end of your seal post with epoxy so you can maintain the speed you are getting now. Without filling the post you will have a gradual decrease in speed as the seal experiences what I call "trampoline effect" and flexes inwards during the shot to reduce compression. Eventually the seal cracks in the center from too much flexing. You might pick up a tiny bit of speed after you fill the post on a newer rifle. You will see more speed if your rifle has seen a lot of lead and the seal has stretched into the post divot. It's pretty much a free upgrade that only costs you a gob of epoxy. The Crosman/Gamo seal change is much better giving you a more durable seal, solid non-flexing seal post and a thinner seal for more volume.
https://target-tune.in/international/pr ... fullSite=1As Rick mentioned, the piston liner is also a great addition to the B3/WF-600. The rifle becomes a quiet shooter without all the annoying spring twang. Just a
thump when shooting. Liners can be made from a large yogurt container or something similar (approx .027" thickness).