Thanks Rick for the suggestion.
I have also followed Ray's method that resulted in recommended 50-minute subs for my 3nm Ha filter...maybe when I get a better mount
So it looks like we really should be aiming for significantly longer exposures if we want the highest practically possible SNR, or for greater number of shorter subs if we want smooth images, but at the expense of detail...
I think that skilful use of TGV Denoise and the like can help to lower noise from long subs with high SNR if needed, but extracting detail from short and smooth subs might be a completely different challenge.