To be accurate, PAM needs to settle to a final value. For 10 bits, you need 7Tau settling; at 2*pi tau per cycle, this bandwidth is just a small amount faster than the channel sampling rate.
For PCM, you need e.g. 10 bits of NRZ or of other modulation method, per each sample. For trustable data recovery, you need to settle to a healthy logic "1" or "0", probably 3 tau, to have wide-open data eye. Thus you need 10bits * 3, or 30 tau. At 2*pi tau per cycle, you need bandwidth to be 30/6.28 or ~ 5 times
the channel sampling rate.
Thus PAM can be usefully slower than PCM, but PCM has much better noise tolerance.