Half that to 8–10 hours? It's only ~350 miles or so, and if we're talking HSR, by the standards of the past thirty years is only a couple of hours or so. The other thing worth remembering is that some of the steepest grades on railways in the world are found on HSR, up to 4% compared with 1.5% that would be considered steep by the standards of most railways.
Fair point about the grade (given right-of-ways for dedicated track). However, it's over 700 miles as the crow flies. It's academic in any case. This would be a project in the $10s of billions and isn't going to happen in the foreseeable future.
