I have ground it pretty fine, but it always made me nervous grinding it. I only ground very small amounts at a time as black powder could technically ignite from grinding. I never really noticed a dramatic increase in igniton speed from what I ground, to 4f and even 3f but I am suspecting there is one.

Like you, when I bought 4f I bought two pounds of it. So I really do not need to worry too much for many years to come. 7000 grains in a pound, 3 grains per flash, = 2333 shots per pound. By the time I finish with the second pound there should be something new to try. Although I am thinking of trying some duplex loads where a small amount of black powder is loaded in the flinter and then you load pyrodex. I thought 10 - 20grains of 4f and then some pyrodex and see if I can get some accuracy out of the rifle.