Longest-range portable 2-way?

Looking for a portable two way that will get you the longest distance? This is our take on it.

Long Range Radio Communications with 5 Watts

How far do you think I will be able to communicate effectively with a 5 watts radio transceiver?
I know that Motorola has handheld radios with 1 or 2 watts transmit power, but I am looking for the longest transmission range possible.
Are there 5 watt radios that I can get hold of that have a longer [...]