I'm pretty sure that there are quite a few ArcToolbox tools that are not optimized to run on 64-bit architecture (at least not yet). Is there a list available that points out which ArcToolbox tools are 64-bit, and which ones are not? It would be really helpful as ArcGIS Pro is still a bit clunky to use (i.e. it pays to prepare one's ArcGIS Pro project in advance before geoprocessing).