You might get some good responses on BROL (BentRider Online).
A few people will be able to tell you their actual experience on the route.
Just search "ROAM" and you will get the names of a lot of participants.
I doubt too many PDX'rs hove done anything near as epic.
I drive the route out to 395 to Spokane a lot. 14 on the WA side is quite reasonable. 12 going into Idaho too is a reasonable cycling route. Once you get past the passes from there, it will be open country roads.