You've already gone beyond my level of planning, so I could probably learn more from you than vice-versa.
On routes, I like the idea of flexibility. While on both the WA and OR routes, I've sometimes found trying to exactly follow the plotted routes to be tedious and the road network in the woods is not static. Instead, I typically use the routes as suggested places to go and modify as I go along. The OBCDR is especially tough in places as it was developed 15 years ago and AFAIK, no one has consolidated all the experiences of folks since in one place; a good 10% of the route no longer exists. There are lots of places on the OBCDR where the plotted route takes off on a goat trail that peters out to nothing, but you can bail on very nice forest service roads and have a great time. For example, FR16 from Seneca to Unity is all paved and the OBCDR route snakes all around it, but only uses it for a few small sections. Personally, I find FR16 absolute bliss on a dual-sport bike so there is not much loss in just finding your own way.
While having a GPS is essential, having good paper maps is also very important as none of the GPS maps available today are very good in accurately showing how challenging a road is, or even showing it if is pavement or grave/dirt. You get into the woods, and the GPS road network spider webs into hundreds of roads with no differentiation of which is the thorough route you need to follow. In regards to paper maps, I don't think any maps touch the Benchmark series for adventure riding - I'd definitely have the WA, OR, and CA (if you get that far) mapbooks along. You can order the forest service maps (or borrow mine if you want), but they're way out of date, bulky, very hard to read, and have too much detail for x-country riding. The Delorme stuff pales in comparison to the Benchmarks.
http://www.benchmarkmaps.com/
My back of the envelope calculations say that if you do the WABCDR from the CND border to around Carson, then trek to Walla Walla, do the OBCDR to Burns, then trek to Happy Camp, then do a typical Lost Coast route, that you'd have about 2K miles under your wheels. Even at a very aggressive 200 miles/day, that would 10 days right there with no rest days, mechanical days, tire-changing/maintenance days, etc. and no allowance for the trek to the start nor the trek back to Seattle. You can freeway back, but that's brutal in one day and no fun in two. Personally, I'd take 3-5 and enjoy some of the great roads along the OR coastal range.
Another issue is camping - since the areas you're in are very remote, you really want to camp, but at the time of year you're traveling, it starts getting dark around 6:30PM. To avoid setting up tents and cooking in the dark, you really want to be shutting down before 5PM or so and unless you're doing hard-core backpacking food, you'll need an hour or so to trek into town and get supplies. Given an hour to tear down camp, your typical riding day becomes 9AM-4PM, and with stops, you'll only have six or so hours on the bike. 200 miles/day in six hours is a 33 mph average, very tough for much of the route where you'll average 25 or so.
Maybe you guys are hard-core, can fix flats in five-min, pound through rock gardens at 35 mph, and break camp in 10 minutes. If so, disregard the panderings of this 58-you adventure rider. But if you want to get full value out your time in WA and OR, I'd recommend you leave CA for another trip or at least consider it optional. It really deserves another trip. Or sorta punt on the whole BCDR deal and just work out a mostly good-through-road route on your own where you can head to CA more directly and stay on better roads and are closer to civilization.
- Mark