Last week I was operating with 50 mW and 5 watt on 80 and 40 meter. Bert PA1B made a wonderful analyse. See for yourself, 5 watt or more is not really needed with WSPR. I think 1 watt or 500 milliwatt will do for 'normal' WSPR transmissions.
Last night I was monitoring 80 meter with JT65A. It was very crowded on the band. Many stations were QRV. I also heard PE4BAS Bas with JT65. He was in QSO with RA6HMS. I called twice, but nobody came back. Too many stations.