I'm don't agree that that the version with unused intermediate computed observables is the only correct version (or that there even is only one correct version)

I'm don't agree that that the version with unused intermediate computed observables is the only correct version (or that there even is only one correct version). Avoiding the use of intermediate computeds makes the Knockout version roughly as fast as Backbone for this specific benchmark, and more closely replicates the functionality of the Backbone example. That sounds like the correct version to me.