It seems that there was a tie-over period when the SP10 firmware was shipped in the earlier 530304288 hardware.
At some point the HG612 hardware was changed, and a new part number (aka board number / barcode) was issued (530313858).
The board was updated with a new flash chip, and maybe other changes.
Previously a Macronix MX29LV640D 8Mbyte parallel NOR flash IC was used but this was replaced with a Spansion S29GL064N. Both chips are in a 44 pin TSOP package.
That change of the flash ID probably required the CFE bootloader to be rebuilt to recognise it. However, the bootloader in SP10 firmware still reports "CFE version 1.0.37-102.6 for BCM96368 (32bit,SP,BE)". That is the same CFE version that was reported in SP06.
The Linux kernel in the SP10 firmware also reports the same version number as the kernel in SP06 (version 18.104.22.168). However, the kernel has been rebuilt, probably with different configuration options.
The root file system also differs between the SP10 and the SP06 firmwares. At some point, I will try to discover what those kernel/file system changes involve.
It would be interesting to see whether the xDSL PHY driver has been updated in SP10.
The Broadcom 6368 processor in the HG612 modem has dual 400MHz MIPS32 VIPER cores which access shared memory.
One of those two cores is exclusively running the xDSL PHY driver. The code for that driver is contained in the binary /etc/adsl/adsl_phy.bin.  The second of the two cores runs everything else, including the Linux operating system. The Linux core moves the xDSL driver code from the flash memory into the address space of the second core. It's possible that if there has been an upgrade to the xDSL driver (adsl_phy.bin) then that could see an improvement to line sync speeds or stability.
The flash dump of an SP10 firmware is linked below for those interested. 
As with SP06, unlocking an SP10 HG612 is very simple. It involves modifying the default config.xml file to remove the iptables rulechain that is firewalling HTTP access to the device from the LAN side.
Edited by asbokid (Wed 20-Jul-11 22:34:08)