I think the TalkTalk experience depends entirely on your exchange and the general usage of the others connected there.
I feel they underprovision the backhaul, maybe in the same way F1 cars carry less fuel than they need for the race (at top power), but this means they can offer a cheaper service.
On LLU 3.5mbit, most things were fine, 1080P streaming wasn't, but 720p was normally ok. Torrents were mostly full speed off-peak, but could crawl between 5-11pm and Sundays.
Have been on fibre for a week now, torrents mostly at full speed (once i'd upped uTorrent cache) not really seen any issues.
Back in the day 1st line support were a pain, 3rd line seemed to be the only ppl able to help with actual fault issues. Not used the forum for faults as I've had none for the past 4 years.
Paying £20.25/month for medium fibre, anytime calls and very happy with current deal (£10.75 per month and £114 years line rental in advance.
For me, my local Fiat dealership, We Are Electricals and BT have been the worst companies I've dealt with.
In theory, theory and practice are identical.....in practice they aren't!