I had a Diana 34 advertised at 1000fps. It weighed 9lbs without a scope. It wouldn't shoot within a quarter at 25 until I bought a tin of 9.5gr RWS SuperMags from Cabela's or on line. It kicked almost as hard as a 2 1/2 .410 and breaking the bbl for every shot became BS. You will have these issues and a bit more IMHO with a Gamo (Gamo quality not on par with RWS/Diana IMHO). Don't be fooled by all that speed and pig killing. They are lucky to group minute of pig's head at 25 using pellets which achieve advertised velocity. The technique for "accurately" shooting a springer is more akin to shooting a bow than a firearm. You don't grip it, you support it to allow for complete vibration. In my fantasies they would be very popular with naughty suburban divorcees. The sensation/noise upon firing is similar to an AR..."booiinnng".
For the same or less jack you could get a used Marlin or Savage long bbl (longer is quieter) .22 and a decent optic without worrying about a Leupold or specific airgun scope: You would reduce weight and noise, not worry about the gun being cocked too long (reduces spring strength); have ability for quick repeat shots and ample energy for close range feral cats, etc (head shot).
A caveat: These rds may triple the energy of a "common" pellet and ALL precautions concerning a backstop MUST be applied as evidenced with the above posted vid. It's quite sobering to hear the strike of the firing pin then a ricochet whine like in a Western movie. I would definitely recommend the Segmented Quiet over other choices. The 40gr bullet may be more likely suited to common .22 twist over the 29 in the CB. I can keep CB's in a nickle at 25: I haven't shot the Quiet stuff yet. The advertised velocity is the same.
https://www.youtube.com/watch?v=I4qE-m-MMx8
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