I think the first thing we need is to clear up the bottle necks where capacity is constricted and speeds limited. Then I would go for a national system of 125 mph DMUs (how long does it take to refuel a DMU?).
Twice a day to begin, then keep increasing service to meet demand. Electrify when you reach a minimum level of traffic. Catenary is expensive to build and to maintain, so I'd want enough traffic to offset the costs with fuel savings.
There are corridors with high enough traffic now to justify HSR. The triangle in Texas, Houston, San Antonio and Dallas. San Diego to San Francisco. Seattle to Portland. LA to Phoenix and Tucson. And much of the east coast.