Using a Fritz 7170 as a router with the ECI VDSL modem

[#1]

Hi
I know there is a really old post about Fritz 7170 from 5 months ago, but I wanted to start a fresh question.
So I have a Fritz 7170 that I was using with my ADSL2 line until last week when I upgraded to plusnet Fibre - and OpenReach provided an ECI modem.
I reconfigured the Fritz to stop being a DSL modem and instead use the LAN1 port as PPoE to the ECI modem, supplying my plusnet credentials to the FritzBox user interface.
It all worked immediately, no problems - except the download speed!
Upload is (nearly) the 20Mbs^-1 I've paid for but the download speed doesn't go above about 35Mbs^-1. The line syncs at 78Mb and my predicted download was 63Mb.
I did a diagnostic, bypassing the Fritz with a regular Windows machine rigged up to do internet connection via PPoE and I get 70Mbs^-1 download!!!
This seems to point to the FritzBox not being able to manage the 70Mb throughput. I have tried setting the DSL speed settings in the Fritz UI to large numbers like 20000 upload and 78000 download (paralleling the line sync speed) but no difference.
So enough preamble: my question is - "has anyone else been using a Fritz 7170 and got a better throughput than about 35Mbs-1??"
If so, how and if not I may have to buy a newer model..

Cheers,
Percussionist Xylo

[#2]

What's your Current Line Speed from the Member Centre?

[#3]

Hi There
my current line speed is 78Mbs^-1 - it always has been.
As I said, when I connect directly to the ECI with a laptop I get about 71Mbs^-1 which sounds fine
I was hoping someone else had the same Fritzbox to see whether it's simply not up to the task of passing data through at 71Mbs^-1!

Thanks

[#4]

There is a post here from someone else complaining of the same issue (in German).
The gist of the reply is "what do you expect, it is 9 years old...".
http://www.glasfaserinfo.de/board/topic,9512.html