Processing speed carries only 10% of the composite weight. It is de-emphasized deliberately. But it serves a diagnostic purpose: your processing speed fatigue slope — how much you slow down across the Diagnostic — is a direct indicator of cognitive fatigue.
A flat fatigue slope means your baseline processing speed holds under sustained load. A steep slope means fatigue is degrading your performance across all subtests, not just processing speed.
Do not train processing speed for its own sake. Train sustained attention and sleep. Your fatigue slope will improve as a consequence.