With those numbers your line will need some work. When I had ADSL from AT&T, my modem bit loading chart suggested a MaxSync of ~5400 kbps was possible; but they capped to the 3008/512 profile.
Ah, found a picture:
SS4100 bit loading chart.
My reported modem stats were 3008/512 with 11.5 dB SNR and 51.5 dB attenuation. Loop length was 9,156 feet.
Alas, I have no screen shots of the ZTE ZXDSL 830II ADSL2+ modem supplied by my new ISP, Sonic.net, LLC. On the same AT&T copper, the ADSL2+ sync rate is ~5900/500, with 6.0 dB SNR and 51.5 dB attenuation.
As your numbers are now, you are not going to do much better than your current speed on their IP-DSLAM service.
I would recommend a post in the AT&T Direct forum. Link this thread, and show them those numbers. If they can do something to improve your stats, that would be helpful. But, assuming the 57 dB line attenuation is an accurate reflection of the loop length, I don't see how they can give you better than 3.0 Mbps service; even with ADSL2+.
Interesting about that modem. I ran the Siemens SpeedStream 4100 for 5 1/2 years with AT&T, and, interchangeably with the ZTE ZXDSL 830II on the Sonic.net "Fusion" service for another six months (at 9,156 feet, I saw no appreciable difference in sync/speed between ADSL and ADSL2+; the benefit of ADSL2+ needs a shorter run of copper to be manifest).
Two others, that I know of, have run nearly as long.
My good friend in the Fruitdale section of town has a Motorola that's been in steady use for about the last four years.--
~Oh Lord, why have you come
~To Konnyu, with the Lion and the Drum