Turbosmooth set to 7 is insane overkill, but ok. I imported the OBJ and reset Smoothing Groups to a single group. I added a Slice modifier to cut away the rest of the model. TurboSmooth at 7. Displace, and loaded your EXR in the OSL Uber Bitmap node. Maybe your import settings need adjustment?
Oh i am sorry i didnt recognize your reply here 12:33AM, really sorry for it. Big thanks to you for your tests. May i ask you to increase Turbosmooth iterations up to 7 or 8 to get sphere 8kk or 24kk? Because it works fine even for me on a low subdivs.