Likewise at 450m with 46meg sync I'm well under the "typical" curve. At least mine is stable, but its always been interleaved.
, from the Broadband Forum, has an interesting graph - Figure 6.
It shows both vectoring behaviour, existing behaviour with crosstalk, and the worst-case behaviour, for the 17a profile on 0.4mm wire. That suggests 100Mbps over 500 metres, showing the Polish results aren't so outstanding.
That graph shows your speed is very much at the worst-case speed for your distance.
ADTran have a "what's next" presentation
that shows a distance of 400 metres for 100Mbps, on 0.4mm wire, but also state that vectored reach should be multiplied by 1.3 for 0.5mm wire.
Finally, Alcatel-Lucent have a paper on their trial results
, showing that recent results are an improvement over early results from 2010-2011. Those trials show 100Mbps at 500 metres, with a statement "Wire diameter and cable type do have an impact on the results and account for most of the variation [...] with commercial equipment".