Crop volume / resample scalar slowness for large image

I sometimes use CropVolume to supersample some of my volumes. For large volumes (e.g., expected size after supersampling is ~20GB), resamplescalarvolume runs multithreadedly (utilizing all cores) and then there is a really long single threaded piece, sometimes taking tens of minutes for the task the finish.

I know the computer is not resource bound (no lack of RAM or anything)? Is it the copying of the contents to the array to the new volume? Would it be sped up somehow?