Here is an analysis of very interesting WSPR spots, that were made by Jaap PA0O. The spots were made from the 19th of oktober until the 12th of november 2015. The band was 160 meter. To reduce the length of the table, I only listed the stations that received more than 60 spots.
The strongest signal was received by G8DYK over a distance of 600 km. The longest distance was 6400 km, to N8OQ.
A Calculated lowest possible power of 1 milliwatt, means that a signal with a power of 1 milliwatt, should be received with a SNR of -29 dB. This is a solid copy in WSPR.
Spots over 2000 km or more.