Brings a smile to my old face; thanks for that.
I used to work in fashion, lo those many happy years ago and part of my work was to provide stand decoration photographs for spring/summer and autumn/winter fashion shows (financed by DuPont/Monsanto as I remember) for a variety of knitwear manufacturers in Scotland. Well, to get to the point of the thread, for black/white it was always 35mm Ilford FP3 (and later 4) in Nikon, but for colour, Hasselblad and Ektachrome. Sadly, Kodachrome 120 wasn´t around at the time - missed that boat entirely.
The 35mm pics were blown up full-width on 40" paper and 60" high. They worked just fine in the location/context/ethos of the time.
Other guys used Kodachrome 25 for the bigger prints, but I always felt that film left too much deep shadow devoid of any detail; too much contrast by far. Worse, colour inter-negs were but another opportunity for something to go wrong.
So how big can you go? There is no definitive answer to a question like that; it all depends on the job you have to shoot, what it makes practical sense to attempt the shoot with and, not least of all, budget. One of the beautiful things about photography is that there IS no answer to a question like this. It all boils down to client, usage and particular photographer. What would David Hamilton´s stuff have looked like if attempted on LF? Sarah Moon in her heyday and those beautiful images for Pirelli´s ´72 Calendar; her dreams for Cacharel? As I say, it depends what you want to achieve.