The RWS/Original Diana 24 is a nice rifle, even if it was forced to masquerade as a Webley (Webley Firebolt anyone? a flippin QB78 innit!).

If you want to extract more power there is a nice nylon piston washer that Maccari sells IF YOU DARE. Longstroke, bigger spring - you could be pushing 7.5 ft/lbs.