CNC machine tool efficiency is all about managing the components that must come together in proper alignment: the machine spindle, toolholder assembly and workspace.
When that inevitable job arises that requires higher RPM output, operators are left with the choice of replacing the machine altogether to gain higher productivity, or looking into an attachment, like a spindle speeder, to close the RPM gap.
Many machine shops lack objective criteria for making toolholder purchasing decisions & most are made by price alone. However they can improve runout significantly by using the right toolholders.