Just as a simple reply, yes you should be able to do those speeds on a good line. Longer lines typically use thicker copper so you should be able to achieve higher sync speeds. My friend has a longer line than you (about 2.5 miles maybe closer to 3) and we got it to sync at 7mbps for a few minutes before seeing problems. We got real world 6.3mbps download speeds on a line with 10dB margins and 51 attenuation.
If they try to leave you syncing at any less than 3mbps/512kbps, they're just being lazy, and if it's at 1.5mbps/384kbps or lower they should be replacing some lines at your distance from the CO or installing a remote.
CompTIA Net+ Network Administrator - I know networks!
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