Sync & Throughput

My ADSL line gradually slowed down to less than 1Mbps. Following an escalation of the complaint from TalkTalk to Openreach, the engineer found no faults as such, but was able to change my line over to a better cable at one of the cabinets (there is a sub cabinet between me and the main cabinet).
As a result of his work, the sync speed at the modem (Draytek Vigor 130) is now over 3Mbps. However, all the speeds tests I perform show 2.4Mbps after the router (Apple airport).
2.4 is as good as I�ve ever achieved on the line. Nevertheless, is the drop of 0.6 from sync to throughput a usual figure?. I am using a brand new 0.5m cat6 cable from the modem to the router, and a brand new 1m cat6 cable from the router to my Mac. The tests were also identical with older and longer Cat5 cables, and are also similar over WiFi.
I intend to try a move to FTTC, but am keen to optimise the ADSL as I�m 1500m from the cabinet, so VDSL may be no better.

In reply to a post by Tertius:

I intend to try a move to FTTC, but am keen to optimise the ADSL as I�m 1500m from the cabinet, so VDSL may be no better.

What does http://www.dslchecker.bt.com/adsl/ADSLChecker.addres... estimate for your address?

Depending on the quality of the copper, you may get a respectable VDSL connection at 1500m.

Before we got moved onto an infill cabinet, we were around 1.5-1.6km from the cabinet and originally synced at 18/4. Crosstalk reduced this over time and it eventually settled at around 13/1.5, but even that is a big improvement over 2Mbps on ADSL.

On ADSL generally allow a 10% overhead between sync speed and throughput as measured by tests/downloads etc

So the drop to 3 Mbps to 2.4 Mbps is not bad.

If the 1500m is an accurate distance then based on what others are getting a lot of the time would expect VDSL2 to exceed your ADSL performance. The results from the checkers are a good indicator normally.

Thanks for the input. It'll take another week or so to complete the complaint process with TalkTalk before moving on to fibre.
Until then I'll live with the ADSL, although the drop is over 20% rather than 10%.

Don't forget the loss quoted is for wired connection to your router. A wireless connection is almost always considerably lower still, as the connection speed between the device and router fluctuates quite considerably even when neither is moving.

It is also amazing the difference between those wireless speeds that results from a move of a couple of centimetres, or a rotation to alter the antennae direction.

Again, thanks for the input. The speeds quoted are for a wired connection from modem to router to the computer, with a 20% loss.

To answer BatBoy�s question, the DSL checker gives:
High Low High Low
VDSL Range A (Clean) 5.4 3
VDSL Range B (Impacted) 5.4 2.2
Until a couple of weeks ago it quoted a max of over 8. No idea why it�s gone down.

In reply to a post by Tertius:

Until a couple of weeks ago it quoted a max of over 8. No idea why it�s gone down.

Perhaps you were moved to a longer line:

In reply to a post by Tertius:

was able to change my line over to a better cable at one of the cabinets (there is a sub cabinet between me and the main cabinet).

That won�t be it. When the fibre estimate went down from max 8 to max 5 my ADSL had already been at 0.7 for quite a while. The line change and ADSL improvement has had no subsequent effect on the published fibre estimates.