Does it work ?
QRP that is. Proved it to myself many times over the years going back to my using a HW8 around 1982. That worked into the USA with around 1.5 watts on 15 meters and rubbish wire antenna.
Had a great demonstration today. I was listening to a Spanish station in QSO with a German station. Initial reports were 559 for the Spanish and 589 for the German station. After a few minutes they revised the signal strength to 569 for the Spanish station and 599 for the German.
No big deal then.... apart from the fact that the Spanish guy was running 5 watts of CW and the German guy was running........ 400 watts !
It could be thought that the German operator's antenna was doing most of the work but... my piece of wet string was receiving both at the signal strengths they were giving out to each other.
When considering if 2.5 - 3 watts is good enough or carrying on to change components, alter coils, etc to get 5 watts then the answer lies in this example heard today. No need to bust a gut trying to squeeze the last milliwatt out of a QCX it isn't going to make a noticeable difference.