Rik - thanks for this - my experiences to date operating from a Central city location in Tiajin China was that WSPR outperformed even dot20 slow qrss in an awfully screen noisy environment - now this was at 500kHz not 137 so QSB etc kinda different.
 
I tried for a long time to catch SM6BHZ on shortpath on all QRSS modes over a period but the only time I have positive ID on multiple nights (really positive not squinting and brain eliminating certain squiggles) was on WSPR using two PC's and a buffered output from the R75 - the visual noise and type of Chinese squiggles made it near impossible to see clearly what was going on - but save on one night when Im pretty sure I had a clean QRSS reception of WD2XNS from over the Pole - conditions that night were "remarkable" from memory -
 
However working out of Singapore/Sabah it was different where visual QRSS outperformed WSPR...different QRM/QRN impulse noises..
 
Different QRM/Source noises appeared to give different results -
 
If anyone is interested the Transpolar North Route to Alaska is still closed (dang it) I can just detect HGA22 visually at dot 60 slow - so some 45dBs or more of attenuation still in place :-((
 
Laurence Kl7UK remotely controlled from South of the Border...