FWIW, the F59PHI's used in Cal Amtrak (Surfliner, San Joaquin, Capitol Corridor) service, and probably Amtrak's locomotives generally, are supposedly designed for running at 110 mph, as are, supposedly, the Cal Cars. Not sure about long-distance Superliners, but they should be good for at least 90 because that's still allowed on (fewer than there used to be) parts of the BNSF route between LA and Chicago. The new diesels that Siemens is building for the various states will be designed for 125. Surfliner equipment routinely runs at 90 (with ATS) on parts of the line south of Santa Ana. That's probably on a par with what Santa Fe officially ran in the olde dayze, though they probably ran a bit quicker when making up time.

Just sayin' ... modern service isn't always as bad as it seems, compared to the steam days, though it's true the long-distance trains are no competition (for timetable speed) even for old-time locals in most cases due to huge amounts of padding. Mostly because of modern commuter service where often little or none existed pre-Amtrak, some terminals (like LA) are busier than ever.

Personal experience on the Cal Cars at 79 on the San Joaquin is that riders would need seat belts, or MUCH better track, at higher speeds than that, and in spots even at that speed. But officially they are designed for it.