I said 125, not 110. The grade $eparation$ are the expensive part. I know this will sound crazy to someone who grew up in a world of slow diesel freight, but give that train some kinetic energy (square of speed) and it will climb the steepest grades without even trying, just by sheer momentum. A 200 mph alignment can follow a shorter and more direct route through terrain with steep ups and downs that reduce the need for tunnels and bridges.
Classic example: Paris-Lyon.
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www.railfaneurope.net]
Top profile is the legacy 19th century PLM line
Bottom profile is the “new” high speed line, shorter and with 3.5% grades
So yes, your 200 mph railroad will not cost much more than your 125 mph railroad.