Answer supplied by Katrina Exter:

The size of the spaxels of the so-called “re-binned cubes” are the 9.4" size of the native spaxel of the PACS integral field unit. The size of the spatial pixels of the so-called mosaic cubes (drizzled, interpolated, or projected cubes) depend on the pointing pattern adopted by the observation: the values range from 0.5” to 3”. 

Definitions of the cubes mentioned here, and the decision tree used when the mosaic cubes spatial pixel sizes were set by the SPG pipeline, can be found in the PACS Spectrometer Quick Start Guide (“Data structure for PACS spectrometer”) and the PACS Products Explained document (Sec 3.2 and 3.5). 

The WCS of the mosaic cubes includes the size of the spatial pixel in the WCS (in HIPE this would be print cube.getWcs().getCdelt1()*3600.0 to get the size in arcsecs). Be aware that the re-binned cubes do not have a correct WCS array.

You can find more information on this topic in the useful Herschel Science Centre short videotutorial on PACS Cubes in Detail. You can find this videotutorial, here:

https://www.youtube.com/watch?v=CxZF9-9D8UM