>These joints caused a 35 mph speed limit on the bridge.

I've always heard this speed limit was on account of the SP red electrics' tendencies to develop a harmonic galloping action on the suspension section at speeds above about 38 mph, which in turn lead to a significant number of popped rivets. The Key units were made of two cars of unequal length, and thus not subject to this. Another consideration was the stopping distance on the eastbound downhill grade of the cantilever section (about which I've read a Toll Bridge Authority report). It also had to do with the maximum number of trains on the bridge at any one time (10 each direction), which was a limitation of the train describer.

Besides, the SP has the same slip joints on the Martinez Bridge, and the speed limit has varied between 30 (frt) and 45+ mph (CoSF) over the years.