You made a point about G.DMT possibly being faster because of lower attn. Firstly the 6.35dB figure is possibly misreported. But secondly ADSL2+ might be showing a higher attn simply because of the way it is calculated, higher frequencies being included in the calculation for ADSL2+ which themselves individually have such a high attn that they are unusable,mand this affects the results of the calculation.
This is the reason why you should always use ADSL2 not ADSL2+, as it excludes the completely useless high bins that do nothing for you but let noise in. (Thanks Burakkucat.) The idea is that changing to ADSL2 instead of 2+ causes a narrowing of the input filters and so lets less crap in.
It might even be possible that G.DMT is a superior performer to ADSL2+, but ADSL2 will always be the best.
Another advantage of ADSL2/2+ is that it can assign a single bit to a bin, whereas in G.DMT the minimum is two bins to a bin, so ADSL2/2+ can use bins that would otherwise just be ignored and wasted for no good reason.