The following info was posted earlier to the popular ThinkBroadband forums:
Hacker Csaba Sipos from Hungary has discovered a slightly newer DSL driver blob for the BCM6368. The BCM6368 is the Broadcom System-on-Chip that powers the HG612 and a good many other VDSL2 CPE.
It seems that the DSL driver version currently shipped in the HG612 firmware is A2pv6C030b.d22g:
# xdslcmd --version xdslcmd version 1.0 DSL PHY: AnnexA version - A2pv6C030b.d22g ******* Pass *********
However, Actiontec, a N.American CPE supplier, has included a slightly newer driver version in a GPL’ed source code tarball for its 6368-based devices . That driver version is A2pv6C035f.d22g
# xdslcmd --version xdslcmd version 1.0 DSL PHY: AnnexA version - A2pv6C035f.d22g ******* Pass *********
It looks like a very minor driver revision, but it might just squeeze a couple more bits per hour!
Anyone interested in giving it a whirl?! Csaba has already built some new firmware with the newer driver, if anyone wants to contact him to try it out?
Over on the Netgear forums,  ARobertson676, Gigio755 and Scubbie have spotted even newer DSL drivers in the beta firmware for the Netgear DGND3700. The latest version with build date 03/06/2012 being A2pv6C035m.d23k
The Netgear firmware seems to have a header on its header, but thankfully the firmware-mod-kit can still extract its components, including the driver blob. The amazing kit was developed by Craig Heffner, Jeremy Collake, Matthias Bucher and others. 
$ wget http://www3.zshare.ma/files/3/82vk2ocjmhtgmi/DGND3700-V184.108.40.206_1.0.20_Static_PPA.chk $ svn co http://firmware-mod-kit.googlecode.com/svn/ firmware-mod-kit-read-only $ cd firmware-mod-kit-read-only/trunk $ ./extract-ng.sh ~/DGND3700-V220.127.116.11_1.0.20_Static_PPA.chk Firmware Mod Kit (build-ng) 0.78 beta, (c)2011-2012 Craig Heffner, Jeremy Collake -- http://www.bitsum.com Scanning firmware... DECIMAL HEX DESCRIPTION ------------------------------------------------------------- 143 0xFFFFFFFE (null) Extracting 321 bytes of header image at offset 0 Extracting squashfs file system at offset 321 Extracting 160 byte footer from offset 8230091 Extracting squashfs files... Firmware extraction successful! Firmware parts can be found in 'fmk/*' $ ls -l fmk/rootfs/etc/adsl/ total 828 -rw-rw-r-- 1 root root 846560 May 12 01:31 adsl_phy.bin $ strings -n10 fmk/rootfs/etc/adsl/adsl_phy.bin | grep -A1 A2pv6 Broadcom DSL Version A2pv6C035m Built on 03/06/2012 17:48:07
EDIT2: See second part of this blog series