It will soon be time to go back to 472kHz. For some reason a myth has grown up that you need very big antennas and extensive ground systems. Also that high power helps! Nothing could be further from the truth.
I can only speak from personal experience. My transverter produces about 10W into 50 ohms and gave about 10mW ERP into my earth-electrode antenna in the ground. My earths are about 10m apart. It has been received on WSPR as far away as Finland and I got spotted in Norway most nights. It was in QST about 10 years ago. It is also described on my website.