For the Walnut Gauge -
I don't pay much attention to gauge height. I look more closely at CFS.
When it's at about 75-100 CFS, Elk and Walnut are usually about prime for my taste - good flow, with some visibility. Fishable (for me) up to about 150 or so CFS. When Walnut's much higher than that up to about 300 CFS, I usually fish smaller water. Elk is generally a little higher than Walnut assuming they get similar rainfall - just a bigger drainage area.
50 CFS isn't horrible - but usually very clear. Much below that and you're talking frog water.
It's all subjective though. What I like might not be what you like or what others like. Those are generalities that I use in planning my trips up.