I suggest you are being unnecessarily pessimistic about possible speeds over Tejon. The big problem is political, with the superior alignment passing right thru the Tejon Ranch at the Bear Trap Canyon and a planned golf course. My understanding is two six mile tunnels and crossing both the San Andreas and Garlock faults at grade and moderate curves so long as they do not have to skirt the holiest of holies Tejon Ranch Co. golf course.

So I think 100mph is feasible over the hill. This is hardly my area of expertise but evidently the limiting factor on speed of the mountain crossing is not the acceleration side but the deceleration. You need to regulate the downhill speed for safety reasons.