Nothing written to back me up, just a little experience talking:
I've definitely seen that 737 AT response is much quicker in ALT HLD once you knock the FMC off the loop. Perhaps it's just because you're cutting out an extra middleman in the chain of command.
I've been asked the CON/CRZ question by a couple of P2s. The best guess I could give them was reduction of engine wear, much like reduced thrust for takeoff and climb. It would be rough on the engines for the AT to keep increasing thrust up to CON for every random speed drop during turbulence. Thus a lower CRZ limit is programmed, which could consequently be jacked up to CON if the situation so demands.
Someone mentioned that TMD remains in CLB during cruise in his planes. That can happen on the 737s too, although it's an anomaly I've observed. When you transition between ALT HLD and VNAVPTH in cruise, I've observed the TMD change to CLB!!!
