I was wondering about the Max Achievable - maybe BT has been pulling user data from the modems ... another source would be DSL Stats so maybe some analysis of the figures there might show something

In reply to a post by WWWombat:

I suspect that the choice for 55/10 at wholesale is that it lets retail ISPs market an "up to 50" product.

There might be a technical reason about which of the D and U bands could get used. But I believe it is as for the reason above, simply so that the product can be sold as 'up to 50' to match VM. A normal user does not want/need to know about the overheads and just wants to see their speedtest result indicate 50Mb.

In reply to a post by Andrue:

No, both their 40/20 and 40/10 products have been withdrawn. They now only offer 40/2 or 80/20 and will not let you have the other unless your line can comfortable sync above 40Mb/s

I believe the 40/10 was withdrawn when they introduced the 40/20 - I don't recall being offered 40/10 when I signed up for FTTC in April (or 80/20) and posts in this thread imply only 40/20 when they went 40/2

Correct. See earlier post.