I never wrote "full speed" so I'm not sure what the quotation marks are for, nor did I mention anything about track geometry, but nevertheless, the metro has a higher average speed than the subway. ATC may indeed help with that."Full speed" is slower how, exactly?
For the record, I believe that the Metro's standard mainline switch is a #6, which would require slower speeds on the diverging than a #9.
ATC doesn't help with track geometry.