I agree on most points, the Gamo was a mistake on my part and you are right about why it is inaccurate. I bought the heaviest .177 pellets I could find to try and help, and it maybe does some, but I haven't found it to help a lot.
On the noise, the supersonic Gamo is louder than a .22 low...
Last year I dispatched 7 raccoons with a .177 Gamo pellet gun. As much noise as it makes though I should have bought a .22cal rifle, more power, more accurate and not particularly louder than the 1250fps pellet guns, quieter if you use shorts.