Route Advice: The Dalles(ish) to Seattle.

Hey folks.

I am currently looking at riding the Oregon Outback route at the beginning of September this year, and then heading to Seattle to visit a friend. I'm currently trying to decide whether I want to rent a Fargo from The Mountain Shop in Portland and ride back to Portland, then train/bus to Seattle, or bring my own bike and just ride to Seattle from the end of that route.

I will be flying in from Ohio, and it seems to be a bit cheaper to rent a bike rather than fly with mine, although if I just ride straight through to Seattle that is probably going to save me the cost of a hotel in Portland and then a train or bus ticket up to Seattle, so it might be a tossup as to the cost.

Any thoughts on routing if I were to ride to Seattle? My initial searching seems to suggest either heading northeast to pick up the Iron Horse Trail, and then taking that towards Seattle, or riding a shorter but steeper route between Mt Adams and Mt. Rainier and into Seattle.

Bike choice if I ride through to Seattle will be my Rawland with front panniers, so singletrack isn't really in the cards.

*edit*
After re-reading Jan Heine's account of doing exactly this, I'm leaning towards riding back to Portland and taking a train to Seattle. The Yakima Reservation doesn't permit people to pass through the western portions of the reservation so it looks like the main way through would be US-97.