Note as well the purpose and theory behind IBL (and, therefore, HDRI). It's intended use is to enable improved composition of 3D array information into a live action scene by duplicating the lighting environment of the actual set in the 3D space. No matter how good the results are when using a probe which is not built to the specific envionment, they will always be better when using one which is specific to the environment itself. For example, in post 4, above, the reflection and lighting would look out of place in an indoor setting. That's the power of IBL.

thou and I, my friend, can, in the most flunkey world, make, each of us, one non-flunkey, one hero, if we like: that will be two heroes to begin with. (Carlyle)