Absolutely serious, but there is one drawback.
First the good bit.
TalkTalk LLU is ADSL2+. The only reason you stop at 8128 is that's the highest ADSL Max goes.
Put those stats figures into
this site but take the
throughput speed with a pinch of salt. On 18Mbps connection I would expect 15Mbps download.
Also look at
this graph, but use 30dB attenuation not your 27dB. Attenuation on ADSL2+ is usually about 3dB higher than on ADSL.
The big drawback is that it is full LLU, where your line ceases to be a "BT" line for other ISPs. So if you ever want to move back it often means a period of a few days with no broadband after the line is returned to BT, plus possible connection charges by your new ISP.
This isn't always the case. Plusnet can move the two together, and I expect BT can if they try really, really hard. But whether you would go to either of those if leaving TT is another question entirely.
Alternatives if you fancy the speed, but not as cheap, are
xilo/uno and
vivaciti which both resell Opal - which is the TT network. Monthly contract and without the P2P throttling. Both are full LLU just like TT.
Xilo don't seem to have it on their website yet. You would need to ring, or PM
uno here. Vivaciti it is the Surfwise Complete. Note the setup and leaving charges.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost.
Internet connection - O2 Standard.