That's rather interesting to me, as I use an ADSLNation filtered faceplate, which I believe has the same filter circuitry as the XF-1e. I don't see the same cutoff in the tone allocation as you do, so I don't think that the filter is actually cutting off those higher frequencies. But it's an active filter, so its characteristics are quite different from the normal passive filters, and your experience may just be that the XF-1e isn't so good in your particular set of circumstances.
I did use a DSL-2740b here for a while, and used Routerstats (full version) with it using the telnet method, but I found the same as you that it often failed to collect a sample from the router and displayed what looked like a lot of dropouts. There was short discussion about this on the Routerstats forum, but it wasn't conclusive.