The highest I've put in was the Haystack Rock bridge behind Crabbe Mountain. If someone would tell me how to get gps co-ords off the geonb map site, I could tell you more. This stretch has some good drops.
Alternately, you can put in lower down where the train bridge crosses the river, at the junction of the West branch and the main branch. There is fast water on this stretch as well.
Some folks have also run the west branch.
You'll need a good rainstorm the day b4.... Good luck!