Sounds like you are on adsl2 on a 21CN exchange, like me. My lines are around 7.3km by road, but I recently read some note by BT that suggested 8km (is that correct from those field notes, Kitizens?) my downstream line attenuation is ~65 - 67 dB. I think your speeds are not too far off for the length of line. My ADSL2 speeds are far higher at 2.7 - 2.9 Mbps downstream sync rate. I have a number of advantages:
* shorter line,
* if I remember correctly it has been suggested that I enjoy very thick copper,
* I would also be amazed if my noise levels are not extremely low relatively speaking because of the lack of electrical activity or civilisation along the last so-many miles (the most critical ones) of the route,
* aggressive modems,
* zero house-internal wiring, no extensions, no phones, and no filter at all,
* totally over-the-top mains-filtering, for what it's worth, if anything,
* Burakkucat's no-ADSL2+-tweak (below) possibly,
* 3dB downstream target SNRM, which is just cheating, trading reliability for speed.
Faster modems might do better, and my own preferred DLink DSL-320B-Z1 modems are very cheap at ~£15 and so if you wish to give one a try then it's only a small financial risk. These are (should be) modem-only devices, not dsl routers, so you will need a router of your choice (with the usual firewall + possibly NAT and maybe wireless too) to go along with it - a two-box system.
These modems are available pre-configured for safe ADSL1/2/2+ operation as modem-only devices from the Andrews and Arnold shop, https://aa.net.uk/broadband-accessories.html
. Do not
use one of these devices as a combined router
plus modem as they have horror security holes, and even with those fixed (poss so with firmware v1.06) they are very bug-ridden and crap as routers so I have been warned. The config will work with any ISP and no login details details are required, you just plug them in and they will work. If you get one, ask about securing the LAN-side admin http interface if the modem is accessible from your main LAN through your router.
However, to get the best
out of them, I would strongly suggest that you tick the BITSWAP tickbox in the advanced ADSL config menu, as for some reason AA are neglecting to do this, and neglecting this should really stuff performance / reliability, unless AA know something I don't about a bug in the UI. If you get hold of one, ask for help with this tweak if needed. A second tweak: Burakkucat has suggested, reasonably, I think, that it might be an idea to also change the advanced ADSL auto-dsl-mode setting to be ADSL2-only, which he and I have done.
By the way, are you on LLU? Who is your ISP?