The French run over 300 mph only during tests (like that last one at about 357 mph). Fastest normal top speed for the TGV is 196 mph. Most of these countries are shooting for about 217 mph (or 350 km/h) in normal service.
A survey carried out in 2004 in the UK
That study is probably biased. If you are worried about kilowatt-hours per seat, increase the number of seats, because the energy consumption will not vary too much. Besides, carbon dioxide has zero effect upon "global warming"; it's an absurd assertion to claim that a gas that exists in trace amounts in the atmosphere (0.03 percent on average) can have such a warming effect, especially since the plants are continuously breathing it in and turning it into oxygen molecules by expiration.
BTW, the nominal power of the TGV is 14 kilowatts per seat. If you ride the train for three hours at maximum horsepower, that's 42 kilowatt-hours per seat. You increase the wattage by increasing the horsepower, not the speed. If your power/weight ratio is within certain bounds, you won't have to raise your horsepower.
(Edit: Noticed the thread on the
DesertXpress thing that I don't think will get built. Sounds like someone's either trying to prove John Mica right, or defy Mica's claim that Amtrak's standing in the way of privately-financed high-speed rail development. The DesertXpress concept just isn't logical to me.)