Originally Posted by
reroll
I am a member of the Frankenbike gear train club and have my own collection of various components, too.
I think the 36T freehub cog was the main attraction of 9-speed, but 9-speed was the beginning of gear train strength and durability compromises, although not by much, and then 10-speed went off the edge of a cliff.
One of the main reasons why 7, 8, 9 speeds are so nice because you can find cassettes with full cogs and not just spidered clusters, so you can mix or match if you don't mind the weight penalty.
My 14-36 consists of a Shimano 14t 11 speed first position cog (ebay), 16t-18t-20t-23t-26t-30t Shimano HG 50 9 speed, I added a Sunrace 36t (9). The theoretical 8 speed cog thickness is 1.80mm and 9 speed cogs are 1.78mm. I imagine the same sheet stock is used for both since .02mm = .0008" and probably within the stock material thickness tolerance. 7 speed cogs are 1.85mm so the max cog difference to 9 speed is .07mm or .003". Even that is within the plastic spacer tolerances I have seen.
John