The VR200 uses a Lantiq DSL chipset.
The VR600 uses a Broadcom DSL chipset, possibly the BCM963268 (based on the GPL source code for the TD-W9970, which happens to also contain a few kernel config files for other models). A Broadcom chipset would be a better match for the Huawei cabinets, although this may not matter much if you are going to easily get the full speed with plenty of room to spare.