I didn't read the whole thread, so forgive me if I'm repeating.
#1: 40 ft is a reasonably large stream. If the stream is truly this large, I'd likely take a 8 or 9 ft 5 wt.
#2: For most "brookie streams", which in my mind are 5-20 ft across and often pretty thick, I prefer about a 7'6" rod in as large a weight as you can find, overlined. I use a 7'6" 4/5 wt loaded with 7 wt line. Purpose of a stout (fast) rod is for throwing tight loops through often tight places, and the need to generate a lot of power with a simple "snap" motion. The reason for overlining is because line weights are based on the assumption of a certain length cast, which you'll almost never meet on these streams. In my way of thinking, matching a 4 wt rod with a 4 wt line is then UNDERLINING, because you're not throwing nearly as much line weight as that 4 wt rod was designed for. So, for instance, putting a 7 wt line on a 4/5 wt rod is actually properly lining it, provided you don't intend to cast anywhere near the assumed distance.
Don't spend too much as these rods tend to take a beating.
And if the stream is really, really thick, then shorter rods come into their own, especially for just easing the movement from hole to hole. Long rods suck to walk with in thick areas. For length, the rule of thumb is "as long as you can get away with and still feel comfortable walking/casting, but not longer".