I use 30lb Braided Nylon for my heavy Trout Shooting Head set up - no issues and it is fine to fish in terms of manageability etc
For Spey Casting for Atlantic Salmon, I am using Orvis Floating Running Line which measures at .034" of an inch (I think)
Some guys favour thinner 0.030" running line but as I tend to use various densitiers of sinking Shooting Heads for colder water fishing, there is a lot of stripping and it is more pleasant to use a slightly thicker Running Line.
Have to say that the best Running Like I have found is the Green and Orange Running Line attached to the rear of Michael Evan Spey Casting lines. These are tops for all round shooting and manageability on a river IMHO