Vector displacement maps can contain negative values (and this one does), so you also need to disable "clamp" under the texture's "colors" rollout. Also, you need to apply rotation since the by default Blender will import Zbrush obj's with a 90 degree object rotation to handle the Y-up/Z-up conversion, you want that applied to the base mesh, not the post-modifier object transform. Once you do that, the correct value reveals itself (it's 27).
Displace Modifier (World Space Displacement only)
vTangent = disabled (world space map, see below if you need tangent)
exr output = on
Flip and switch = 27
Mode = RGBtoXYZ
Midlevel = 0.0
Scale = 1.0
Coordinates = UV
Apply rotation after importing to bake the axis flip, but DO NOT apply scale. (if you apply scale, you must compensate with the modifier's scale setting)
Displacement map (texture panel)
Color space = non-color ("linear" or "raw" should give the same result by default, but are technically not "proper")
Clamp = disabled
Tangent Space Displacement
In Blender 2.8, Cycles includes support for vector displacement. Unlike the displace modifier, this system DOES support tangent-vector maps. The node setup will look like this. Note the use of "non color data" on the image texture. In most cases, the "vector displacement" node should be left at exactly these settings, they are the defaults for a reason.
Tangent space maps are not dependent on the object transform, and can also displace meshes after they have been affected by deformation modifiers such as armature, corrective smooth, curve, etc. This is extremely useful when rigging a sculpted character from Zbrush. You can rig the level 1 mesh, then use subdivision and tangent vector displacement to rebuild the high-level sculpt at render time after deformation has been applied.
Note that as of Blender 2.80, adaptive subdivision does not support mesh tangents. As a result, you will need to use fixed subdivision with tangent-space maps. (if your object is not going to deform and you'd rather have adaptive subdivision, you can still use the same world space maps and settings you'd use with the displace modifier with Cycles vector displacement shader. Just change the vector displacement node's space to "object" or "world")
In this case, export your map from Zbrush with the following settings:
vTangent = enabled
exr output = on
Tangent flip and switch = 25
Whether you apply rotation or not does not matter with tangent space maps.