1. Take West Point's first point: "Getting rid of all the slow sections would be a good first step. Yes!! Yes!! Yes!!
There are many. many examples of 79 mph speed limit railroads with several miles of 30 mph or less into major cities, sometimes with a couple of 10 mph sections. Simple arithmetic: 1 mile at 10 mph takes 6 minutes. 1 mile at 60 mph takes 1 minute. Every mile of 10 mph track you can upgrade will save several minutes, as there is slowing and acceleration times to be added. Years ago one of the writers on this subject in the Railway Gazette International stated, "The best way to go fast is to avoid going slow." Some of the Brits I know refer to this sort of thing as a pronouncement by the Bureau of the Blooming Obvious. I can think of several examples in Amtrak schedules, such as on the Texas Eagle route look at the length of 25 mph limit out St. Louis. Worse is the round about slow speed trek into and out of San Antonio. Many terminals have strings of 10 mph to 15 mph turnouts in and out. There are AREMA standard turnouts, nothing exotic that can be run at 25 to 40 mph. Yes, it would make for a longer ladder, but if you have the space, use it.
2. If you are laying out a new HSR, do go for 220 mph or even more. Although right now anything above around 186 mph (that is 300 km/hr) seems near irrational, that may not be true in the future. Remember, when the Japanese started building the Shinkansen lines, 200 km/hr (124 mph) seemed like the edge of the planet so far as speed on rails is concerned. Obviously that is no longer true. For example the Taiwan High Speed Rail was opened and runs as a 300 km/hr operation, but everything alignment related can safely and easily go to 350 km/hr, that is 217 mph for those wanting their information in normal units. If new alignment, set your curves and spirals, and vertical curves for 250 mph at least. You can always open with a lower speed limit. Having a 250 mph alignment does not keep you from having a speed limit of 125 mph when opening. Two important points: Be as straight as possible. A straight line has no speed limit. Remember, the Roman roads are where they were built over 2,000 years ago. What ever you build, you will be stuck with from now on, so don't fold to pressure and insert doglegs in alignment that in 10 to 20 to 30 years or more have people looking and say, "why did they ever do that? It makes no sense."