Leo, I would stick with the 30lb running line, especially since you like it
In my opinion, anything for salmon, even steelhead for that matter should be around 30lb ... to make it the strongest part of your rigging.
Fly lines are usually rated around 25lb, some higher and some a little lower. Your tippet will be somewhere between 8lb and 20lb. This way if anything goes wrong, it will be the tippet or part of the leader that will break, saving your fly line, etc.
I would only step down to 20lb running line if I was chasing smaller species, like inland trout, bass and walleye.
If your worried about shoot-ability with a lighter head, than maybe contemplate mono type shooting lines and still keep that higher pound test rating.
You mentioned that you were planning this for a smaller salmon river, so not sure how far you need to cast to get your presentation to the salmon ... ??
Just some food for thought my friend