Other aspects to consider about antenna gain
A higher gain antenna does not create more power than the radio produces on its own. Antenna gain increases or decreases signal directionality.
Looking at antenna charts demonstrates the signal pattern of an antenna. Notice, the higher the gain the more directional its signal pattern becomes; think Yagi antennae.
Consider your location of use, then chose the appropriate antenna.
Using an example of an adjustable lens flashlight (torch) such as the Maglite: Remove the adjustable end exposing the bulb only, notice the produced light may fill a dark room; think low gain antenna. This why a lower gain antenna is much better in an urban area, in areas with much more obstructions, in forests, and the like. That is why many folks in locations with buildings, many obstructions, forest, and the like, when switching to low gain antennae have better TX and Rx signal reports as well.
Now connect the adjustable section and its lens to the flashlight, adjust it. Notice it is now concentrating the light in a much more directional beam. Now the light does not fill a room with light; it performs better pointing into the room; think high gain antenna. The higher gain antenna performs better in less obstructed areas, such as open roads without obstructions, mostly flat landscape and the like. Thus, in considerably more open unobstructed locations switching to a higher gain antenna will increase its reach. Keep in mind, the radio is outputting the same power to the high gain antenna as it does to a lower gain antenna. The difference is the high gain antenna is creating a more directional signal.
Yes, the above is an odd example, however I hope it makes sense.