I'll let others speak to the PNW proper (WA/OR) but having moved from way southern oregon recently I'd say your best 4+ish bets for that time of year are (South to North):
Trinity (Burnt Ranch Gorge may be highish)
Cal Salmon (the section with Frieght Train may be lowish)
Klamath River (Hells Corner dam release weekends only)
Deschutes (Meadow Camp, Lava, Dillon something will be just right)