This is purely a scholarly or theoretical question, so assume minimum line lengths and perfect attenuation figures.
The Wikipedia article on VDSL2 states that when using the 17a profile on VDSL2, it's capable of connecting at 100Mbit/s.
So, why do people within a stones throw (~50 metres) of their cabinet get the "maximum" speed of 57MBit/s?
Is this due to DLM? Are the Chorus reducing the connect speeds for reliability? Is it something else?
Edit: Does this mean that the DSL reports DSL speed calculator is unreliable as at low (below 9dB) attenuation figures are reported at >58MBit/s