For what it's worth, here are some numbers I googled on the Calgary-Edmonton corridor:
NPV of revenues (min-expected-max) from
Oliver-Wyman report (billions of 2006 $):
125 mph: 1.4 2.1 3.5
150 mph: 2.8 4.3 6.4
200 mph: 5.6 9.2 14.3
300 mph: 13.5 17.0 24.3
And the costs, estimated by the
Van Horne Institute (billions of 2011 $):
CPR line (comparable to 125 mph) 2.5
Greenfield non-electric (comparable to 150 mph) 3.7
Greenfield electric (comparable to 200 mph) 5.0
300 mph (maglev) isn't costed, but based on these numbers it looks like a 200 mph Calgary-Edmonton train is just about can't miss economically.