I was getting less than 1 Mb/s last week. It's over 10 Mb/s now. Th esite I use to test uses Flash graphics it was putting a strain on my CPU and using all the power. Web pages download to your hard drive and so a low hard drive like on my old desktop slows things down too. I have a Phenom dual core with loads of memory and a SATA 2 hard drive now and I optimised my TCP. It would be faster and i may phone and get the line adjusted, it noisy and the LCP (link control protocol) on my router drops and I lose sync on the ADSL sometimes.
The number of phones shouldn't make a difference if they are modern and not excessive. I have 1 old one and 1 modern base running two cordless; it doesn't make a bit of difference.
This graphic shows my speed a few minutes ago: http://www.speedtest.net/result/899714915.png