Bolt action air rifle power?

im looking at getting an air rifle and saw the co2 powered bolt action smk's which were fairly cheap. does anyone know if these are any good or not? i saw somewhere that the power was only 6ft/lb? is this right? im going to use the rifle for shooting vermin such as rabbits, pigeons etc. i like the bolt action rifles but in fairness its the aesthetics. does anyone know of any higher powered bolt action air rifles? im in the uk so the legal limit is just 12ft/lb. any ideas? or would a breakbarrel gamo real-treehunter be a better option for me? cheers