Sorry if i sounded sarcastic, i really wasnt trying to be. i am just hoping to learn from your experience. every "unbiased" article i can find indicate the 42t cog are working great and most show a xt or xtr RD. I would love it, if it worked with shimano, which is what i would really love to use. finacially im probably only going to get one shot at this, so im trying to do my homework. the 42t cog, seems like it makes all the difference to get me in my needed ratios, and the 40t leaves me wanting. i wish the makers of these cogs would just say it works great with these RD's and so-so with these. but they dont seem to indicate any problems at all. which is why i was wondering if you tried calling any of them as they might have some solution you hadnt thought of or just admit the problem. i appreciate your quick response and insight.
you are right on the 16t cog, not available by itself yet. 40/42 seem on back order. and i believe if you bought a 40/42 previous to the 16t cog, you can email for free one.
thx again, for your time