Checking Broadband speeds

I have used several web-sites to check my broadband speed, most of which give downstream & upstream speeds. However Test Result (http://www.speedtester.bt.com) gives 4 speeds -
Can you please explain them:
DSL connection rate ……… (downstream) 448 (upstream)
IP profile for your line …………
Actual IP throughput achieved during test ……….

The final figure ('actual IP') is usually close to the readings I get from other sites such as broadbandspeedchecker.co.uk and I guess this is a reasonable measure of my working download speed.

The DSL connection downstream is usually larger than the actual IP, (but not always).
The DSL connection upstream is always 448 kbps and greater than the upload speeds measured on other sites.

However the IP profile for my line is the one that interests me most, it stays constant for days then seems to change - I've had speeds of 4500, 3500, 2000, 1500, 750, 350, 250, 135 - my internet provider is BT, and I wonder whether they, in some way, make changes to this 'profile'?

Your help & advice would be appreciated

Im not positive, but I believe DSL is effected by many things, quality of the lines, distance to the switch. Traffic.. etc

The speed tests don't matter that much anyway. Its rare that you will get those speeds on anything :) most sites don't have the speed to allow that high. Im on Cable and my speed tests have hit 9000, (at work I can hit over 20K) but the most I have ever hit downloading was a file from MS was around 800K