Wow, sorry it took me so long to spot this thread. Now that I'm here I'll have a whack at answering your question. Whe you say you're a fan of the Walker action I'm assuming you are refering to the big 16'6" sticks? If so I might suggest you consider the 13' 3wt in addition to the 12'6" 4/5. When I first cast the 13'er last year I was immediately struck by the similarity to my 16'6" 9/10....only a LOT smaller and lighter. Sort of that relaxed, on the fast side of progressive - firm in the butt, action shared by several of the Walker series. As far as the line weight goes I tried from 275gr Nextcast troutfinder FF with a variety of tips up to a 390 Rage and Aerohead 5/6. Basically everything I have that might be remotely appropriate. The little troutfinder was the only line under 300 gr I have at the moment. what I can say so far is that the 13' 3wt. has a pretty big grain window leaning to the heavy side. It is extremely smooth and quite powerful for a trout rod and really easy to cast. Nothing tweaky about this little stick, it feels like a real rod. It's great for swinging wets and has no problem with modest sized streamers (e.g. unweighted size 6 marabou muddler) which is about the biggest I tend to fish.
The 12'6" 4/5 is a slightly stronger rod by 25-50 grains and also has a broad grain window. With respect to action I would say the two rods are a little different. In a proportional sense, the top half is a little stronger on the 4/5 than the 3wt. So I suppose by definition the 4/5 has a slightly slower action. It sort of reminds me of a little 16' 8/9 powerlite. It's easy to cast and readily handles a wide variety of line styles. When the Trout Speycaster line of rods was first conceived 11'4" 3wt was intended to be the "soft hackle rod" and this 4/5 was to be the "streamer rod". You might think of the 13' 3wt as the "greased line rod" if you will.
Hope this is of some use. Feel free to PM me if you have any questions.
TMc