en.wikipedia.org
While there is unfortunately some cross-tolerance, benzos only seem to affect the binding of GABA, while barbiturates affect how long the pores are open for. Despite that, apparently someone who's more tolerant to benzos is more likely to be sensitive to barbiturates in other areas (something to do with barbiturates also being AMPA receptor blockers and interacting with nAChR and voltage-gated calcium channels), but I dunno if that affects the mechanisms that barbiturates can lead to CTBing.
Maybe someone who's better at biology/chemistry will have a better idea of whether benzo tolerance can negatively impact barbiturate overdose CTBing or not?