Verified answer

not enough that you would ever notice the additional 1.5dBm

Free space loss is : L = 96.6 + 20log F + 20logD where F is if in GHz and D is in miles. For a 10 mile path the loss is 124.2 dB. If we add 1.5 dB and solve for D we get 11.88 miles or 1.88 miles more on a 10 mile path. Since the result is nonlinear we can calculate that you will go 3.7 miles further on a 20 mile path and 5.5 miles on a 30 mile path.

Since we do not know the transmit power and the receiver sensitivity (or the line losses) to determine the system gain, the we cannot determine the path length you can achieve including an adequate margin for fading. The system gain minus the free space path loss needs to be a positive number with some margin for fading losses.

You may know that one of the 2.4 GHz channels is in a ham band. Some hams in Virginia put together a 37 mile system, but I forget whether they used an amplifier and some dishes.

By the way antenna gain is not measured in dBm, just dB. Also, a 38.5 dB gain antenna is pretty big at 2.4 GHz. What are you using?

Good luck and have fun. 73 from the Fisherman

In "practical applications" like your home (where 802.11g is typically used), the difference would be insignificant.