Whatever the theoretical limit is, they're pretty much right at it at this point. Similar to how ADSL2+ was near enough at the theoretical limit of what the fre

Whatever the theoretical limit is, they're pretty much right at it at this point. Similar to how ADSL2+ was near enough at the theoretical limit of what the frequency spectrum it used could do given the attenuation it was asked to do it at. For the same frequency ranges as ADSL2+, VDSL2 delivered pretty much no improvement. What VDSL2 did do is expand the frequency range up to 17 MHz/30 MHz, depending on the profile. So the question you might want to ask is "How high a frequency can we use?" and in that case the real question you're looking for is "How short a piece of copper do you have?". And the answer to that is very quickly becoming "a very short piece of copper indeed". Either that or a lot of copper that's ideally also very thick... which, considering most copper was rolled out with the aim of providing a low attenuation at 3000 Hz over at most a low number of kilometres isn't often the case. tl;dr: How long is a piece of string?