Digital BW, The Print

After 2-3 years of digital darkrooming and B&W printing I am still 
not happy with my methods to darken blue skies.
I am familiar with the red filter / polariser filters on film 
capture, but my efforts to successfully replicate this digitally 
have never been particularly fruitful.  I have tried many channel 
mixer, hue/sat methods to convert my digital colour images to B&W 
but all result in some sort of posterisation or noise in the sky.  I 
cannot get a smooth dark sky.  Selective darkening also is very 
difficult if you are really trying to go dark, the halos/  edges are 
almost impossible to avoid.
Even after running neat image or selective bluring to remove sky 
noise I end up with clear banding in the sky as it gets darker.

Anyone want to share how you get those really dark / black skies 
with me, any real way of doing this from a digital colour file?  

I know this is slightly of topic but most of the 'retouching' or 
editing forums are populated by colour gurus, this is really the 
knowledge base for B&W.

Thanks
Steve