Just came across this thread, but a well established kitesurf downwinder is south of fort stevens/astoria. Did it with wingfoiling back in june. Starts- wreck of peter iredale and went 8 miles down the coast to surf pines. Numerous beach access points along the way for shorter rides.
Conditions parameters were <3 ft at <8 seconds. Some shorebreak but was easy to time a window through. Wind was 15kn, side on shore. 5m wing. Was a blast.
Look forward to doing it again next summer.