5 miles is "best case". VHF is line of sight. Range depends on a lot of things besides power and probably the biggest is height off the water.

At the Hobie 16 NAs in the Nevada desert, there was a small hill between the host hotel and the main part of the lake where the boats were. No radio reception. Even if you went to the top of the hill, it was difficult to hear each other even though we were only 3 miles away.