I was down in the Key Largo area last summer. It was a diving trip primarliy but while there I visited a friend who was living down there (since moved back upstate). We went shooting iguanas two afternoons. Plus took a few off the porch. The big ones are harder to put down than I had thought, head shots do it but if you put one through the shoulder not so much. I know JSB is releasing some new .22 heavy pellets but otherwise, I would go .25 and the heaviest pellet available which is the JSB 34 or possibly their new, if released, Heavy Hades 36 grains pellet. I would not feel over gunned with a .30! That said, the smackdown a .25 gives vs a .22 pellet is huge IMO.
The rifles I brought were my two favorites, a .22 Urban (26 fpe) and my Marauder Super Light .25 (60 fpe). These two here:
As to the .25 being more dangerous to people and property, well, I have not observed that .25 flies much further than a strong .22. Pellets are just not ballistically efficient. But if you plan slugs, either caliber, could be a problem. We made sure we had a solid back stop to our shooting. Shooting in the direction of people and property with an expectation that a .22 pellet will probably not reach so far, not sure about that.