(I put this in the general forum topic, as well....)
Combinations of .003 and proph (.0025) seem to consistently work best for me and for those I make calls for. The thicker latex never seems to produce the same sound quality, although I am sure there are callers out there that prefer .004 and thicker. For the "average caller", however, I think using .003 and proph combinations is the way to start off. You should plan on experimenting with the thicker latex though,...just to see how it works for you.
I like .003 layering for both two and three-reed calls with reed backsets of 1/8" +-. .003 over proph can be just as good. Reed cuts are equally or more important, as well. Keep your cuts to the longest (sound) reed initially. Also, I suggest moving your reed cuts to different locations along the reed when cutting your calls to find your "sweet spot".