On my 52.5dB 3 mile line (INP 1.4 to 1.6, variable, with 2700HGV), a 2Wire 2700HGV/HG-B will sync above the 5120 required for a 4500 profile, but invariably retrains after a few days to somewhere between 4600 to below 5120, depending on the time of day/night. My profile is therefore usually 4000.
An ST585v6 or Homehub 2A will sync about 4800 - 4900 and stay up forever - again a profile of 4000.
I generally stick with the 2Wire for its superior stats, user info, etc.
YMMV, of course, and you may find
this of interest.
Edit: FWIW my DSLAM vendor is TI - reportedly it can make a difference with certain router/DSLAM combinations.