This is the original 5 stop tonal range.

Nearly everything is beneath the mid-tones (green), which are minimal. And there is a vast sky of highlights.

I'm getting more and more confused about changing from colour to b&w with Dan's recommendation of channel blending, when one has to blend and curve different channels in 'normal' mode before switching to Luminosity.

So here are the 3 channels, in decent sized images - Red, Green and Blue.
There is not much difference between the Red and Green channels.
But the Blue is really different, and I do not see much noise.

This wee image is the difference between the Green and Blue channels.

I think we can slightly improve the far mountains by applying the Red (or Green) channel into the Blue in Darken mode - so I'll do that and then de-saturate - giving this image, which is a very slight improvement (not really worth writing home about).