It was great fishing with you as well...hope you did not mind the local 'culture' (if you know what I mean).
Anyways, Juro has hit it right on.
I am usually of the Stilly by mid-August (my home river) and have made my way over to the Sky. The Upper Sky is filled with aggresive hatchery steelies in September and the SF Sky above the falls has large numbers of trouty aggresive wild summer-runs.
And then you have the coho in the saltwater which can be awesome...
And sooner or later the Wenatchee will open back up which is arguablly the best summer-run steelie river in the state...especially if you are flyfishing.
The nice thing about September is that the waters have cooled a tad, and late summer showers have woken up the summer-runs from their warm water hiding places of August.
The first two weeks of July can be AWESOME on the Stilly but the river is small and does get crowded...but with the hatchery fish returning again to upper river, July would be an excellent choice and I will do whatever I can, to assure your trip will be a success.