as you say these are always going to be relatively modest in output but to get the best out of them is really as already stated by posts above;
over powering is nearly always a mistake,the meteor spring replacement is the most advantageous then replacing all the performance related parts
like breech seal and piston seal,the piston seal in leather is an overlooked item in terms of performance and yet very simple to get the best from.
both sides of the excess can make a noticeable reduction in output;a lesson a friend learned when rebuilding his much loved airsporter ,it was what we thought at the time a little to tight and even when a fair number of running in shots were fired power was down ,after a tad was removed from the sealing faces re lubed and she was running at full power consistantly ;the other often detail overlooked by newbies is the pellet choice.at the "range" a demonstration of a wide variety of ammo in 3 very different airguns with a detailed chrono check was an eye opener for me returning to the sport .and showed me to overlook this can spoil even a quality mark.
[FWB124s]-[ORIG45]-[relum rescue ctr][bell trgt maker]
I CAN RESIST EVERYTHING EXCEPT AN FWB,