As I read your graphs, the Mk3 degrades S/N above about tone 4000 , roughly 17 MHz ?
This is academic for anyone on any version of ADSL and many on VDSL too in the absence of interference. With appreciable interference, the loss may be acceptable to give a nett gain on S/N+I on the lower tones.
It cannot be over stressed that NO filter is lossless; so don't jump up and down over a slight interference loss. I am in the situation that a 2 bit dip on tone 46 is due to the Droitwich transmitter. It can be removed with a RF3, but there is a slight nett loss.
In basic English "You can't have jam on it !"
Les - We all owe you thanks for finding the limitations of the RF3 type devices.
BUT, and I think you agree with me, it should not put off anyone on lower BW VDSL or any ADSL from using a potentially useful device.
It just isn't a magic cure all !!!