60db does seem correct, it syncs at about 3300 which is comparable to my work connection which is approximately the same distance (although on a different exchange).
The only thing I can think is that there's burst interference but I'm at a loss as to why DLM hasn't intervened with a higher SNR or Interleave, I even tried resetting the connection by pulling the plug 4 times in a couple of minutes, but it still didn't raise the SNR target.