Well I've been assured by an Openreach Broadband engineer the line has more potential in it, I've been speaking with Plusnet and they are willing to give this a go.
I'm being swapped from an 8mb product onto an ADSL2+ product, and then on Monday my target SNR for downstream will be set to 3db and upstream to 6db, my interleaving will also be removed,
Then I and Plusnet will be monitoring the line for errors and issues and will act on it from their, I'm pretty confident that the line has more upstream sync speed in it, and maybe another 3-400kbps downstream but if I notice any issues or any significant error rates being reported I will be requesting that the lines SNR targets are set to 6db for both up and downstream and that the lowest interleaving setting is set to reduce them.
The worst that can happen is the line ends up slowing down until it can be reset to more stable settings.