Where have all the Selectrics gone?

134.5 baud was the exact baud rate required to match the motor speed of the main shaft in the selectric mechanism. At that speed, the printer main shaft clutch would remain continuously engaged. At any other speed, the mechanical wear would destroy the mechanism VERY quickly. Obviously, with buffering and handshaking one could use a faster rate externally, but that speed was essential at the mechanism level. All selectric mechanisms, at the mechanism level, use tilt/rotate code. You tilt the ball to select a row, and then rotate it to select a column, then whack the paper through a ribbon (it's a mechanism that Tony Soprano would love). That is simply how a selectric works, and any other code will ultimately get converted into tilt/rotate before being applied to solenoids in the mechanism.