Hi Kev, virgin is fairly unlimited - and has fkn good speeds these days
I've done A LOT of downloads (legal of course but much more than your
50gb) on the wire and i've heard nothing from them to say stop...
Plus, it's a more reliable service imho
if adsl is a must, don't overlook be broadband - O2 most likely have a
reseller deal with BT or someone else, like orange have... so they
wont want you using their bandwidth which they pay BT a fortune for
(did you know 1gb over limit can be charged at about £5/+vat by BT)