I suggest that the optimal Tejon, I-5, Altamont, Dumbarton default route could break even with sustained operating speeds around 160mph. Basically express. I like the median because it would make it harder to add any stations.

Just the SF & SJ run to Sac via Dumbarton and Altamont would be significantly faster than the Capitol Corridor.

If you want regional commute just go Amtrak diesel and engineer the Tehachapi mountain crossing as a king of improved Loop line with ruling gradients around 2% and no tunnels that diesels could not handle. Later it can be repurposed to freight.