Getting optimal speed?

Hello
When I ordered broadband with Sky, they estimated a whopping 20mb for my line. Now it's up and running it's at 13mb. It's acceptable, good even, but I'd like to make sure I'm getting the best speed. Here are my stats:

ADSL Link Downstream Upstream
Connection Speed 13470 kbps 948 kbps
Line Attenuation 29.0 dB 17.1 dB
Noise Margin 6.9 dB 8.0 dB

Putting your attenuation in here:
http://www.kitz.co.uk/adsl/max_speed_calc.php

Suggests a maximum sync speed of 16000 kbps

If you have a test socket within your BT master socket plug your router in there and get the stats again. That will show the best you can reasonably expect.