Not BT here, but...
... the ISP-supplied does-everything-and-n-too* box gets 3, 3.5, maybe 4Mbit/s (down, and 440kb/s up) on a good day. A much older modem-only box** actually gets somewhere north of 6Mbit/s (down, and 1024kb/s up). Apparently the other power requirements, perhaps for the wireless, detract from the ADSL interface, as I've seen progressive generations of ISP-supplied kit*** perform worse and worse, with ever fancier features such as voip, iptv and 802.11n support added. Basic ADSL and IP routing function, even simple firmware stability, even without any of those fancy features actually seeing any use, suffered. Their mere presence was enough.
All of which just to say: Might be worthwhile to try a separate ADSL modem with a sturdy power brick, and do the rest with some other box.
802.11g, while nominally 54Mbit, will only see 20-odd Mbit in practice. It's half-duplex and shared, after all. And depending on how your situation (did you do a site survey?) you might improve local reception quite a bit with something as simple as a bit of cardboard with tin-foil backing stuck on an antenna. See eg freeantennas dot com for inspiration and even a nice printable template or two.
Of course, all that is far too practical and doesn't drive more sales, so obviously releasing more "pre-newest-standards" kit is the way forward. I haven't really kept up but various free OSes don't even have full and proper 'n' support yet. Glad to see someone going forward, eh.
* Though of course no 5GHz. Or QoS, or current line usage, or showing which MAC eats the most bandwidth, or a host of other little things that would in fact make the ruddy thing *useful*. No alternate firmware either.
** For political reasons it cannot be used, and neither could a sensible ISP. So crappy Arcadyan kit and KPN it is.
*** Then thomson, with fantastically bad firmware that violates the gpl to boot. The replacement is different, but not better.