m8 dont get draged into the "i can do a steady 20 bps bullsh1t" as most can't,infact most can't do more than 15
.they may spike above 15 but cant keep it there(if they say they can,ask them to do it over a decent chrono
)
anything over 6/8 bps constant will lead to you freezing up(the old mags and cockers would/will do it)
air is easyer to fill,use,more available at tourneys and far more consistent,ie air will do +/- 5 fps over a chrony,co2 in the same gun will be +/-15-20 fps
you can get a new air system,ie just screw in same as co2,for £68 new so why bother with co2 as a new co2 system is £40 alone