[star_juice]

Alright, you win: this answer is fantastic. This is a far, far better way to think about what limits scalability than simple things like pages served per millisecond. I never did expect to find ready answers that will guide me to making the universally scalable app, but now I see the problem can be reduced even further into niche sorts of scaling which, while solvable with hardware tricks, do their very best to escape generalization.