Every rod is a compromise. With a 9' rod you will find spots where you'll wish it was longer. Looking at some of your photos on the other thread, I think there'll be places you'll think even the 9' rod is too long.
It seems most of the people who write books about small streams compare them to rivers like the Madison or Delaware, and figure if you can't take a drift boat down it then it must be a small stream. They don't write about streams the size of yours because they assume most of the guys they want to sell books to would think they are unfishable.
In Dave Hughes book, he does talk about fishing with short tenkara rods, including the Kiyotaki 24, which is 7'10".
http://www.tenkarabum.com/kiyotaki-24.html Tom Davis, of Teton Tenkara, has done a number of Youtube videos of fishing small streams with that same rod or the Nissin Fine Mode Kosansui 270, which is in the TenkaraBum Small Stream Starter Kit http://www.tenkarabum.com/small-stre...arter-kit.html Both links will take you to pages that have Tom's videos.
Those rods will allow you to fish relatively tight streams. For the little wild brookies in your mountain streams, I would choose the Nissin Air Stage 240 http://www.tenkarabum.com/nissin-air...iryu-rods.html over the Kiyotaki, though. It is a much softer, more sensitive rod, and better matched to the 5-8" fish you probably catch.
I would choose a line no more than a foot longer than the rod, though. The longer the line the more you will get snagged on your back cast. You will have to be exceedingly stealthy, though, to catch much with an 8' rod, 9' of line and maybe 3' of tippet.
One other choice that few people here have tried is to use a very long rod and extremely short line and just drop the fly into eddies and seams - essentially dapping. It is called "lantern fishing" in Japan and is used in the extreme headwaters there. You will not be able to raise the rod to bring in a fish. You have to collapse the rod instead. I've done it a couple times and have caught fish that way. It is very, very different from standard tenkara, though.