You should be able to get the modem to tell you what the maximum attainable rate is for your line, what the current rate is and what mode it is operating in.
You had to use a service mode password for the old Speedtouch I had. I'm not sure what you'd do for your newer one.
I made a Python script to extract the data from my modem to put it into MRTG. I can see the noise margin going up during daylight hours and then down again when it starts to get dark.
Mode ADSL2
Down Up
Current Rate 644608Bps 120448Bps
Max Rate 662528Bps 120320Bps
Capacity 97% 100%
Noise Margin 8dB 6dB
Line Attenuation 48dB 28dB
Power 0dB 12dB
On ADSL1 I was at ~3Mbps but its gone up to ~5Mbps by switching to ADSL2.