It's always the stats we need to give a good idea of expected speeds

. Speedtest results are affected by too many things.
But!
Why on earth aren't you already on O2 LLU? It's great - any bad reviews or ratings are because of the non-LLU O2 Access.
You would get ADSL2+ immediately, with no BT aggressive IP Profiles and noise margin management. It is true unlimited with no traffic management and you expect about 84% of connection speed at all times. (70% during World Cup and Tennis).
O2 Premium is £15pm, or £10 if you can quote an O2 mobile phone number against it. Currently three months free, and expiring today or tomorrow £75 cashback through Quidco or TopCashBack.
So that is at most £60 for the whole first year, and possibly as low as £15.
You can sign up through those two sites without a MAC and supply it later. Just make sure you
clear cookies first.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost.
Internet connection - O2 Standard.