Fabian,
Pianka and King's "Varanoid Lizards of the World" is not intended to be a new contribution to monitor classification -- instead, the classification used there (mostly) follows the most recent formal taxonomic treatment of the family. That reference is W. Boehme, 2003, Checklist of the living monitor lizards of the world (family Varanidae), Zoologische Verhandelingen (Leiden) 341: 3-43. Boehme recognizes the three subspecies of V. albigularis mentioned by Mark, with ionidesi (from Tanzania) being considered part of V. a. microstictus.

Unfortunately (and inexplicably), Jennifer Ast did not include any V. albigularis in her DNA-sequencing analyses (2001, Cladistics, vol. 17) of the phylogeny of varanids.