Robert's comment about aperture size is quite relevant here. At a fast shutter speed where the opening/closing of the leaf shutter takes so much of the total "open time," the efficiency will be markedly different between a wide-open aperture (least efficient) and a very small aperture (most efficient). I would think it would be important to do your shutter testing at the aperture(s) you use most.
I know that I rarely, if ever, make a photograph at an aperture smaller than f/22. I'd say more than half of my exposures are made at an aperture somewhere around f/32 (give or take a third of a stop), so I'd likely test at f/32.
Having some way to measure the total volume of light instead of just the time between the first glimmer of light to make it through the opening shutter and the instant it goes dark would seem to be necessary to really get meaningful exposure data with a leaf shutter at high speeds. Maybe Dan's suggestion about asking your reversal/transparency film is going to end up being the most practical after all...
Best,
Doremus
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