DiegoD, as I recall you are in Puerto Rico. Sorry but I don't know how big iguanas get there. I think the .177 at 750 fps is going to be fine for thin skinned small game at home ranges. I would look for a higher velocity if I was after squirrels, but I have no clue if you have those down there. Squirrels in my area are tough skinned little beggars. I would stick to the 177 at that velocity, and get pellets that will penetrate. Get your rifle zeroed, and some practice, and let us know how you do. For bigger birds I used to do head and neck shots, back in the day (many decades ago!) when I had pellet and C02 sporting arms. I think the 22 pellet is at a disadvantage in penetration unless you can crank up some serious velocity, and those rifles are pricey. Buena Suerte.