I woudn't get too hung up on the range calculations as it is only an approximation. Lots of other variables play on actual distance within which you will have reliable communications including sea state, weather, tropospheric ducting, angle of the antenna w/r to vertical, nearby metallic objects effecting the antenna radiation pattern, etc..
Most VHF marine radios are equivalent although some microphones may not be creating the perception some radios are inferior. Conversely, all coax is not equal and can have a FAR greater effect that one might think. Some so-called marine coax has a significant power loss compared with good quality RG213 and as it ages, the loss increases. Poor soldered connectors also have a major influence on the radio's performance.
In all, don't worry about the radio - it's all about the installation.
Most VHF marine radios are equivalent although some microphones may not be creating the perception some radios are inferior. Conversely, all coax is not equal and can have a FAR greater effect that one might think. Some so-called marine coax has a significant power loss compared with good quality RG213 and as it ages, the loss increases. Poor soldered connectors also have a major influence on the radio's performance.
In all, don't worry about the radio - it's all about the installation.