I guess it must be line specific...but in my experience it's the exact opposite. I'm on an ECI cabinet, normally using a Broadcom based modem. Due to a noise burst over the w/e I'm on high interleaving, banded at 15Mb. As a test, I just switched back to my Lantiq-based HH5a and got a DS sync of 10706 @ 6.1 db - ping to bbc.news.co.uk was 50ms. Immediately put a VMG8924-B10A back on the line and got a DS sync of 14563 @ 6.3db - ping to bbc.news.co.uk was 30ms... (Normally I'd hit the banding of 15000 but at this time of night the SNRM is very low so sometimes it syncs just under). I've previously tried a Draytek 2760 and got a similarly poor DS sync, although I didn't try a ping as I just wanted to put it back in its box and return it to sender!
Probably line specific, though I can't comment as to the performance of the HH5a. I don't trust ISP supplied and branded equipment
. Lantiq/Infineon chipsets tend to sync slightly lower on fastpath, possibly on traditional interleaving too. For fastpath it's due to the fact they apply an 'R' (reed solomon coding) of 16, a light form of error correction. The Broadcom chipset doesn't seem to do this on fastpath (R: 0).