The one disappointment when I changed modems from the DLink DSL-320B-Z1 to the ZyXEL VMG 1312-B10A devices has been the loss in upstream sync rate. I got 560kbps u/s sync rate on one of my lines but now that is down to 500k, a loss of 10.7%. On one of the other lines 500kbps dropped to 440kbps, a loss of 12%. The other line showed no significant speed change.
I wonder why this is?
But looking back at historical records, I see that the upstream sync rates obtained further back in time with the DLink modems were about what I get with the ZyXEL devices now. The high upstream sync rates I was enjoying more recently have been an off-again-on-again phenomenon.