Unless your system is timing out, speed should not be an issue for regular webpages. If the webradio is supplied separately by the ISP it's one thing but I assume you just mean it online, which require the downloading of a page no ? Maybe it's new on me, but I would think all of this uses the same frequencies, and webpages loaded a long time before there was streaming audio on the net.

No matter what I would repeat the test a whole bunch of times. First of all every time you disconnect the thing the modem has to reacquire the signal, and who knows what happens then in the way of what error correction might be applied.

Also note that DSL, which is usually ASDL, is not all that fast in the first place. Uverse might be different but if it has to come through a phone line it has to come through a phone line, period.