I just tried several modems on my line and by far the best performer was the ZyXEL VMG1312-B10A. Others I tried were the BT Openreach modem, TP-Link TD-W9970, Billion 8800NL R2. The TP-Link is not a bad performer but let down by wireless performance.
I would suggest looking on eBay for a ZyXEL and giving it a try as I have gained about 5 meg sync since plugging it in after a very quick setup. Note the B10D its replacement has a cheaper broadcom chipset in it and is the same chipset as the TP-Link and Billion.
My sync speeds at 5dB
TP-Link - 64/17
Billion - 62/17
Openreach - 62/17
ZyXEL - 71/17
I just tried several modems on my line and by far the best performer was the ZyXEL VMG1312-B10A.
The OP doesn't need a modem router. He already has an Ubiquiti Edgerouter which is up there with PFSense on features. The Zyxel, and all the others you list, are [consumer] junk compared to it.
OP - your sync rate was obviously just increased by the DSLAM deciding to lower the target SNR. My target SNR recently fell from 7 to 3/4 resulting in a gain of 3-5Mbps. Same as you. This has nothing to do with your equipment and everything to do with BTO's DSLAM.