Yes, VDSL2 uses the same symbol rate as ADSL - 4000 symbols per second.
The raw bitrate comes from summing the bit-loading on each tone in the two directions, and multiplying by 4000.
There are roughly 2750 tones used to carry downstream data. If you can add one extra bit to the loading of every single tone, you add (2750*4000) bits per second, or 11Mbps (Hence my rule-of-thumb mentioned earlier).
There isn't really a concept of 8 bits per byte that deep down in the VDSL spec. It is, instead, just a bitstream - a steady stream of bits, allocated to be sent on the tones according to the bit loading allocations.
At higher levels, the packet of user data - somewhere between 64 and 1500 bytes that we understand to be 8 bits per byte - is converted into a bitstream at 8 bits per byte. However, the user data ends up embedded in surrounding overhead control and protection data, and gets encoded in various ways, which ends up padding out the bitstream somewhat. FEC is one such additional overhead, and interleaving is one such form of encoding, though there are more.
The end result is that, for every byte of user data - every 8 bits - you need just over 8 bits in the low-level bitstream being allocated to tones. At best, it might be 8.01 bits in the bitstream for each byte. With high levels of FEC turned on, it could easily reach 9 or 10 bits for each byte.
Unless, of course, you are the lucky recipient of @kitz's data. If it isn't arriving at her modem, it must be appearing as extra overhead on someone else's.
I wonder if there's a tagging issue going on, with VLAN tags going wrong somewhere.
