Based on my (limited) experience, I'm not sure it's quite that simple...
I have a Billion 8900AX-2400, which syncs at a (banded) 14999 DS. The SNRM at first sync is around 8dB if I sync in daylight or 6.5dB if I sync at night - drifting down over time to around 6.5dB during daylight hours and 4.5dB at its lowest over night.
I briefly tried a Draytek 2760, at a point when I knew from my Billion that I was banded at 14999. Without tweaking the SNRM offset on the Draytek, it synced at 11400 (ish, can't remember exactly) - I know that looks like a banded limit, but I immediately switched back to the Billion and was straight back to 14999. Based on memory (I don't have detailed stats that far back), when my line had been banded at 11400 in the past the SNRM when my Billion first synced was in the region of 12dB. I just gave up on the Draytek (sent it back) without really looking at stats or playing with parameters - didn't seem worth it since the starting point was so poor - but my guess would be that if I'd played with the SNRM offset it may have got me back towards the 14999 that the Billion achieves without any tweaking. i.e. no gain.
Has anybody tried back-to-back tests between a decent Broadcom modem and a Draytek to see what really happens? I don't doubt that playing with the SNRM offset improves the sync on the Draytek, but what would the sync have been if a Broadcom-based modem had been used w/o any tweaking?