OR 58 is not very bike friendly, plus the DOT will be rebuilding a tunnel near Willamette Pass starting this month, which will cause major delays. This tunnel work may be a blessing for bike travel due to the many trucks that use it choosing another route. I wouldn't say don't use 58, but I've never found it to be a nice ride.

I'd suggest Eugene to Oakridge, then take Aufderheide scenic highway to McKenzie Bridge, then Old McKenzie Pass (Rt 242) to Sisters. This is one of the best rides in the world, so.
I can make you a best route map from Eugene to Oakridge if you'd like.