ADSL2+ Slow Sync with Thomson St585v6/ST780

I have ADSL2+ (BT 21CN) and am close to the exchange Line Atten 20/12 S/N 6/6.
When I connect either my Fritz!box 7390 or 7270 or Technicolor TG582N The Sync is 16.5/1.050. However if I connect either Thomson ST780 or ST585 v6 the line syncs at only 2 - 2.5 mbps download and correspondingly low upload speed. The Thomson routers show ADSL G992.5 which I believe is ADSL2+ they also have the latest UK firmware 6.2.29.3.

I found that if I use the CLI Command to force the ST780 into ADSL2 mode instead of ADSL2+ it syncs at 10.5.

Question is does anyone know why these routers don't work properly in ADSL2+ mode.

Incidentally I tested the same ST780 on my line back in December and it synced at 16.5mbps. Same story at my neighbours with the same router - used to sync at 16.5mbps now 2-3mbps unless forced into ADS2 mode.

Have you looked for later firmware versions?

Why on earth would you want to use very ancient routers? Granted, Speedtouch ST series were very good ~10 years ago but modern routers are using far superior chipsets.

Also, you should be getting a sync of ~ 20 meg on a 20 db line. My line is longer than yours (29db atten) yet i'm getting 17.5 meg on a 6db SNR.

Thanks for responses.
With regard to Firmware - as stated there is no later firmware available.
With regard to more modern routers the ST780 has unique appeal as it is favoured for VoIP use at low cost - I only use it as a backup to my Fritz!Box but I am keen to find out why it doesn't work correctly with ADSL2+. It seems that the problem is not unique to my setup as I found this post at Whirlpool:
http://forums.whirlpool.net.au/forum-replies.cfm?t=1...

It has the latest firmware - there is no newer FW. I also tried older FW's - same probllem.