This is just me, but I would probably do something like Trans-Am to Sierra Cascades south to Crater Lake, then out to the coast from there. I love the Columbia Gorge (on Lewis and Clark route), but there is one big drawback during summer months: a pretty reliable and STRONG headwind heading westward. You may get some headwind on the Trans-Am, but it probably wouldn't be as severe as it could be on the L&C.
And I find it a little funny that you titled your post "How to get through WA" when you're mostly talking about Oregon.
