To render fast spinning motion blur effects at the OBJ level, you need to increase the transformations MB steps. Sometimes you could need 10 or 20 steps to make it work fine. On the other hand, the fast spinning deformation MB at SOP level (from mesh deformations) is not possible currently because the deformations MB is using only two steps.
Hope it helps,
Computer Graphics Software Developer
Octane plugin development and support: LightWave and Houdini