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Sam --
No, photographing gray cards is not a very effective way to get good exposure and/or development information. The best method, by far, is to study the film's characteristic curves. If you'd like to tell me what film and developer you're using, and give me your email address, I might be able to send you an appropriate film family that will illustrate what "pushing" actually accomplishes.
"Push" processing is really a misleading title because it implies that extending development can somehow increase the sensitivity of the film. Unfortunately it can't; all extended development can do, in most cases, is provide a modest increase in effective film speed (in the order of half a stop or so), while dramatically increasing image contrast. This is not really a "push" because that's the film's normal response to extended development.
When you follow the usual "push" recommendations you're really underexposing and overdeveloping, and if the "push" promises a speed gain of more than a stop you're almost certainly going to lose shadow detail. In other words, the effectiveness of "pushing" film depends on your tolerance for empty shadows and harsh gradation.
There are a very few film/developer combinations that show some appreciable increase in effective film speed as development is extended, and without building very much contrast. Bergger 200 sheet film is one example that manages a speed point shift of more than two stops as development varies from 4 minutes to 16 minutes. Trouble is, its claimed ISO 200 speed is wildly overrated and even when "pushed" to 16 minutes it barely reaches an effective speed of 100.
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