Great looking render, really like it!
Generally I advise against rendering with defer atmo, but I guess you want it in order to get the cleanest result possible, isn't it?
So what are your current render settings and especially AA setting?
I found out that 16 atmosphere with AA8@1/16th still performs reasonably well.
However, when clouds come at play and especially >1 cloud layers then this will change quite drastically.
My approach to testing this would be to test it on a per cloud layer basis and after finding the optimum for each layer render a crop "for real".
Quite likely, because of shadows from one cloud layer to the other, the result will have some more noise, but I estimate an increment of 0.1-0.2 for cloud detail will fix it then.
What you should keep in mind though is that with AA8, for example, the pixel noise threshold is 0.0375. If the pixel noise drops below that no more AA will be applied.
However, there's a chance you still see grain and you think you need to up the cloud detail, but there's still grain when doing so.
Likely, the AA value along with the pixel noise threshold (which actually determines how clean the result is) cause it to still be noisy.
Then you would need to up AA and start over again (a bit) with determining the cloud quality.
So perhaps it's wise to first see if your AA value of choice will give you the result you're looking for, before you're starting to optimize endlessly without realizing the AA value might never be able to give you the result you're looking for.
You may now understand why I advise against RTA and especially when you do so with clouds, because first of all it's complex and secondly it barely ever is faster than non-deferred rendering. So instead of experimenting for hours with RTA I just render it with several dozen of atmosphere samples and high cloud quality and I'm sure it will look fine. Kind of "fire and forget".