Good point. I remember, but have failed miserably to find it, a web site that had a graph of signal strength plotted against noise. It showed that at the very limit of reception little changes in level produced by antenna, or power at the transmitter had a big impact, but this point was fleeting. Add just a little bit more and noise dropped very quickly. Effective comms always takes place in the signal level range where changes to level make hardly any difference. If your comms path requires you to stand on a chair, hold the radio above your head and wave a leg in the air to create a better ground plane, then a teeny bit more power the transmit end might do some good. Once you are in the good area, then jwilkers is correct, power is almost irrelevant, and we have plenty of evidence to prove it. Half a Watt got me to an astronaut, yet going up to 60 Watts from 5W wont get me to a workplace from my office, despite being one post code away! My own sort of rule, is that if a signal is so weak I cannot quite understand what is being said, then if they are on low power, going to high is worth trying. 3 to 5, or 5 to 8 is hardly worth swapping the radio. 1 to 10 might be detectable, as jwilkers correctly points out. dB’s are a good way to think it. If you cannot make more than 2dB difference, dont bother!