Are you sure the two ADSL lines are going to the same ""box in the street" and from there the same exchange? I used to have two BT lines, one went to Wimbledon, one to Kingston - no way to tell until one failed and the engineer that was sent out pointed it out to me.
BE what's their name used a lower contention rate to achieve the higher bandwidth IIRC.
It might also have something to do with ADSL2 as opposed to ADSL.
As for AOL
I wouldn't trust the online tests either - too many variables to distort the figure. All you need is their server to be doing a backup or sumethink.