I think the best result is somewhere between the two. They both are artificial to a degree, there's a halo around the entire bridge in the first, which I'm not sure if that's what you intended, but almost seems to give away dodging under the bridge to bring the brightness up; you want to avoid general indicators of your work, unless you desire that artificial look. (I've seen a lot of 'building halos' recently, which makes me think this is a new trend?) The second is an example of VERY high contrast, but only in some areas? You've got a good tonal quality on this one (much less 'flat' than the first in the shadow regions), but the shoulder seems a bit abrupt - b&w film has a softer shoulder and can bring out some details in that pure black area, i.e., there would be some subtle toning in the shadow there. (Although, admittedly, this LCD is very high contrast and I might be missing some detail here.)
Another trick you might do, if you notice your levels/curves/channel mixer causing high noise in sky scenes like that, esp. after applying sharpening, it can be fixed without recognizable artifacts by something like noise ninja after all other processing has been done. I use this on my skies about 90% of the time when I'm not going for a 'grainy' look. Make sure you flatten the image first, then dupe the layer, run your noise reduction across it, and mask out anything that isn't sky. Your skies will end up properly smooth (but not too smooth), without losing detail on cloud fringes.
Here's an example of doing so:
http://shutterdrone.wordpress.com/20...reef-cabin-ii/
And here's an example of not masking out the water after applying the NN filter:
http://shutterdrone.wordpress.com/20...ehabilitation/
(Mind you, I've since fixed the water in this image and the blown cloud, but I try not to be too 'revisionist' about blog postings.)
If you'd like, I'd be happy to share a step-by-step detailed process of how I go about this. Maybe some extra tricks to add to your arsenal?
In truth, there's nothing "right" about how to do it, there're simply objectives and a handful of strategies for obtaining each. My process is intended to emulate pink-filtered acros 100 film, which is what I shot before going digital. Either way, you're very much on the right path.
!c