Another test. Simple scene with ground plane and the Pink Evening Spectral Sunset. Converted to Photometric Spectral in Vue 14 = 20 min 55 sec, and the same scene in Vue 14 spectral render results = 10 min 28 sec render time, and, then, Vue 11.5 = 10 min 4 sec.

I was doing a bunch of other stuff while the render was running so that could account for  some of the difference. The 20 percent mentioned above was from a scene with no clouds and non volumetric sunlight which the Pink Evening Sunset does have.

The new atmosphere is a little confusing. New scenes open with no sun for some reason and light and atmosphere settings are still somewhat cryptic so there is still a good deal of ambiguity about it all.

Hopefully there'll be more results showing up around the web soon.