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.
Banding can change on the fly when your swapping modems back and forth.
I'll eat Paddys hat if the Draytek didn't hit a banded figure. Probably over 5000 to 1 odds it resynced at that exact number (11,399 you've stated on numerous previous posts).
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
14,999 @8dB snrm would be 19-20Mb attainabnle
11,399 not banded (6dB) would be under 60% the sync rate of the Billion.
The Broadcom chipsets do tend to perform better/sync higher than Lantiq.
I don't believe the difference to be anywhere near that high though.