Will changing phone number improve sync speed.

Here is a puzzle. Our office is about 5km from the exchange. At moment we have an ADSL line (Zen on BT) that syncs and works reliably at about 2Meg.
Decided to install a second line (Plusnet on BT) but can't get more than 500k even after trying a number of different routers.
Samknows is showing the first line as "1.5m" and the second line as "256k if lucky" yet it is showing the same distance and same exchange for both.
The first three digits of the second phone number are different. Does that mean it is just plugged into different equipment in the exchange ? Or does it mean the cable takes a different route to our offices from the exchange ? Or both ?
Main question is how on earth do we fix this ? We can only talk to BT about the voice service on the line - which works fine. Plusnet can only talk about the data service on the line - which is within spec for that particular number ?!
Help !
David Watermann

Question is are the line attenuation figures about the same or wildly different?

The phone number tells you nothing about the routing, and the line checkers are no good for this, you need to compare actual data from the ADSL modem - NOTE: Not results from speedtests either

http://www.kitz.co.uk/adsl/frogstats.php shows how to get the numbers from most hardware

There are no guarantees that a line will perform at a specific speed or better, in fact BT can refuse ADSL if they want. If the second line is connecting at 576K down, and 288Kbps up, then they've put you onto a fixed speed product, hence why the speeds don't vary, changing to a variable speed product may make you go faster. Seeing the stats will let us estimate this.

Both are pretty bad. The new line is showing attenuation of 63.5 down. The existing line is 62.5 down
Moving the same router between the two confirms there is a big difference. The old line router stats show a Downstream rate of 2816 K and Upstream 448 K. Same router on new line struggles to sync and at best shows a Downstream rate of 512 K.

Zen sent me these stats for the existing line:
The connection is currently in sync as follows ;

Loop Loss: 33 dB
SNR Margin: 19 dB
Errored Seconds: 0
HEC Errors: 0
Cell Count: 2068
Speed: 448

Downstream
Loop Loss: 62.5 dB
SNR Margin: 7 dB
Errored Seconds: 1
HEC Errors: 0
Cell Count: 2992
Speed: 2880

And Plusnet sent me this for the new line:
Upstream Link Info
Loop Loss 43
SNR Margin 8
Speed 416

Downstream Link Info
Loop Loss 63.5
SNR Margin 8
Speed 544

BIP Interface Data
Current line rate 350
Maximum Stable Rate Recalcuated N
Maximum Stable Rate 576
Fault Threshold Rate 576
Interleaving Flag I
ServiceOption 1
ServiceOption Status T
HIS LINE IS STABLE AND WELL WITHIN ERROR/RETRAIN LIMITS FOR THE CHOSEN SERVICE OPTION (ILQ=GREEN)

Plusnet have put you on a fixed 512 kbps connection. It doesn't matter what router you use, you'll only get the same sync speed.

No they have not if the info "Speed 544" is correct, a fixed speed would connect at 576Kbps downstream.

Looks like one line is marginally longer than the other, and in short there is nothing you can do. Changing the number will not help, and unless you have a few £1000's to pay Openreach you won't get a shorter line or re-route.

As I said BT is at liberty to say take this speed or we can turn it off.