Well, I managed to get TalkTalk to install an unbundled line at my house and its slightly faster than BT's, and seems to be more reliable. However it still only connects at 1.6Mbps and not the 2.4Mbps they estimated, although there does seem to be some room for improvement as their settings allow for much more room for error than BTs.
I've kept the BT line as well, and have subscribed to the SharedBand bonding solution
www.sharedband.com. This combines both lines together into one for the computer's purposes. Its not bad, but it doesn't seem to be a 2+2=4 answer, more like a 2+2=3.3. For my business though it does make a bit of a difference and we can now download and get up to 250Kps rather than 140 before. I am not sure if that's worth it for an extra £30 per month but will have to stick with it for 12 months.