Did parts of the route twixt Baker and John Day several times last fall in the toad while the coach was parked at Unity Reservoir. Pix of 7 can be found at this link
http://www.milebymile.com/main/highway-67.html .
Jerry's description pretty well describes it. We've been over it in one coach or another over the years, as I like coaxing small trout out of the "crik" below Phillips Reservoir and other waters in the area, exploring the Sumpter venues and nearby ghost towns, and driving the forested hills. 7 should be no great challenge, but watch for crazies anxious to pass on a few slow curves on the hills; When a couple-three cars build up behind, I look for a wide pull-over big enough where I won't freak out the missus by suddenly hitting the brakes and swinging over the shoulder.
An option is to take 26 out of Vale/Ontario; it's more on par with 20. The only part of 26 that bugs me is between Mitchell (I think) and Dayville where the two-lane road meanders through narrow canyons that keep me on my toes. You'll end up on 26 anyway when 7 ends, so be aware of that, although it may just be my peculiar nervousness in such driving scenarios.
As an aside, we like Prairie City better than John Day, if you're lookin to overnight somewhere and toad around a bit. It's not as busy a place, is less the tourist town JD's become, and has a less-expensive, nicer public RV park (Depot Park). You can buzz down to JD for supplies and a Dairy Queen if need be, than cruise back to P City easy enough.
Joel