I think you're still getting your 'B's and 'b's mixed up badly... 1.5MB/s equates to about a 12mbps line... not 4. Peak throughput on a 4mpbs line wouldn't be much higher than 450KB/s, taking overheads into account
Well BitTorrent reports that I download at 1.5 MB/s.
My stats:
DSP Firmware Version E.25.41.55 A
Connected true
Operational Mode G.Dmt.BisPlus
Annex Type AnnexA
Upstream 511800
Downstream 4095900
SNR Margin(Upstream) 34.5 dB
SNR Margin(Downstream) 32.00 dB
Line Attenuation(Upstream) 2.0 dB
Line Attenuation(Downstream) 9.0 dB
Very odd indeed. The downstream is definitely 4Mb/s, so you shouldn't be able to exceed that. What BitTorrent package are you using, maybe there's a bug in the speed code and it is reporting Mb instead of MB.
Only other things I can think of is if there is another computer with BitTorrent on it on your network and part of the download is coming from that machine as well or to make sure you're not connected via a cell phone somewhere.