Saw this movie on Sunday at the Landmark Theater in the Westside Pavilion...
I've always liked the use of Super-16 for color period movies set around the turn of the last century, even though there really wasn't a true 3-color process back then. The grain and softness create an organic "filter" for the image that removes it from the contemporary and evokes older processes like 1940's Agfacolor, autochrome photographs, etc. Some movies have achieved this with push-processed 35mm and older optics -- I've always loved the Little Italy scenes in "The Godfather Part II" for this reason, especially the shots made near dusk on the streets.
"Suffragette" was shot in Super-16 cropped to 2.40, with low-light night scenes shot on the Alexa on softer optics and with grain added in post. Day interiors were still shot in Super-16, even some large ones and some low-light ones. The combination worked rather well, though a trained cinematographer can spot the differences.
The Super-16 was timed on the pastel side, soft blacks and colors, suiting the period, and in general there is sort of a bleakness and somber cool tone to almost everything. Only occasionally did I feel that the widest shots of the city streets in daytime looked a bit too lacking in resolution (particularly the first time the film cuts wide), otherwise the softness was pleasant in tighter shots, again evoking older film processes without resorting to diffusion filters. There is a race track scene at the end which is a bit sharper and less grainy than the earlier scenes, I assume either because the sunlight helped with overexposure or perhaps they switched to a slower stock.
It's funny because I never used to notice this until digital photography became more prominent, but one clue that you are looking at film is that bright edges often have a reddish fringe to them. Now perhaps this is an optics issue as well because I've noticed this effect with Cooke lenses, but in general, overexposed edges around lights and windows often have this warm fringe with film.
The night scenes had a very realistic look, shot in very low light levels on the Alexa. Your first clue that it was shot on the Alexa is mainly that the depth of field is much shallower being a 35mm sensor rather than Super-16, but considering the low light levels, my eye accepted it as typical of the results of using fast lenses in such situations. And despite the softer lenses used, the shallow focus, and the grain added, sometimes the Alexa images are still sharper than the Super-16 ones, but in general, it blends pretty well, helped by the fact that the two formats are shot in such different circumstances -- cool daylight versus flame-lit dark interiors.
The movie is shot in a semi-documentary style, deliberate roughness in the moves, sometimes "grabbed" moments, but it is consistent.
The movie shows that Super-16 is alive and well, and perfectly valid for productions of this scale.