It is not that hard to build hollow tube conical shafts with a relatively small bearing at the bottom and a large external bearing at the top. This solves the question of shaft bending and shaft harmonics while still providing a large bearing separation distance, if desired. My equatorial mounts all have these homebuilt conical shafts in the polar axis. Typical dimensions for a scope to 10" in size would be bearing separation = 20" and conical upper bearing diameter = 20". The upper bearing then only needs to be driven by a roller bearing, resulting in a very smooth and accurate drive.
Mel