I would suggest what i did and first make area renders before you render the whole image. Probably with godrays i would think you have to give a quality boost in the sky-fog-haze tab and maybe also some quality boost in the lighting tab.

Keep in mind the large render times when upping these boosts ! As you can see on the two examples i posted and the render time that came with them :-)

I can 't say what is better for this, volumetric or spectral mode because as i said before, when it comes to render settings i 'm still somewhat of a newbie LOL !

 

Society failed to tolerate me...

... and i have failed to tolerate society