RE:Spey Rod Size?
My rapidly dwindling Spey exposure per annum concluded the following before I left the wild west...
Started with the 14' 9'er like everyone else in those days. Fun, but wanted a 15' 10wt so sold it and picked up the Sage 10150-4. Hit the Skagit and a few other rivers that size... LOVE IT! It casts dense winter heads easily. It casts DT's and windcutter lines easily too. Very sweet rod, almost sold it - GLAD I DID NOT!
Then got my hands on a 7136-4 for summer. Sweet! Hooked and landed a lot of summer fish on it and got hooked on the lighter and shorter feel (to your point!). Fished it into the winter... started to hook bigger spring nates and find out that it is not easy to get the thick wire winter hook penetration needed with the little noodle to hold big fish in big water. I really do like the lightness and ease though. Needed something more stout for spring fish in smaller rivers.
Third: found an G.Loomis IMX 15' 4pc 8wt rocket launcher. It is a perfect in-between the other two. It casts a head, Windcutter, DT, etc.
I am pretty happy with the mix I have going right now but if there were a shorter rod with the same pop as some of the longer Spey rods I would welcome it in my arsenal.
Who makes the 13ft 9wt you have?