When first searching for a short backcountry/small stream rod I remember thinking that I wanted something no longer than 6' maybe 6'6". After handling a few that short and doing some pretty serious thinking, I realized that something slightly longer would suit me a little bit better both for my casting as well as the streams. 7'6" just fit me and my situation a little better. I now have a 7'6" glass rod as my small stream rod. It seems to handle whatever I throw at it whether it be very tight cover or the large pools that I sometimes encounter.
To me your length should match your wallet and your situation. Weve all come upon spots where we think, "Man, that 5'6" 2 wt would be perfect right here!" and then get 100 yds upriver to find that your 9' 5wt is what you need. We cant carry every rod we own along the river like a set of golf clubs. (although that would be awesome to have a fly fishing caddy!) A balance has to be found between fundage, application, and practicality.
I know opinions are like....well.....you know what. So theres mine.