That's a very good question, and one for which there is not a simple answer. On the surface, one might assume if you use enough of, say, potassium carbonate in place of sodium carbonate, such that you equal the required pH value, the result would be equal. In fact, I believe, using those chemicals, that would be the case. I think I recall from one of Anchell's books that as long as you stayed within a given familial group (ie: carbonates), substitution was predictable.(posted 8334 days ago)However, simply matching pH while straying outside the familial circle invites interesting deviations from the expected. For example, sodium hydroxide is noted for producing high pH values. But what one seldom hears is that the high pH value falls rather quickly, and thus, is very valuable in compensating formulas. Carbonates, on the other hand, maintain a more consistent alkalinity and a steadier buffering factor during the cycle of development. The net effect is surprising. I've found developers using carbonate often exhibit more contrast and more grain than the same developing agents used with NaOH. This is quite the opposite of what I was led to believe from various published sources. Try substituting a 5% solution of NaOH in place of potassium carbonate as the "B" component in FX-2 to see a very pleasing case in point.
I know I haven't really answered your question, Conrad, but hopefully I will have opened lines of thought that others may contribute to and from which we may all learn.