In terms of theoretical peak
raw performance, cable
modem generally wins the
speed battle over DSL.
Cable technology can, in
theory, achieve networking
speeds of approximately 30
Mbps (using a 100 Mbps
network interface card),
whereas most forms of DSL
cannot reach 10 Mbps.
(VDSL is one variant of DSL
that matches cable's
performance, but it is not
generally available.)
In practice, though, the
speed advantage of cable
over DSL is much lower than
might first be apparent.
Both cable modem and DSL performance vary from
one minute to the next depending on the pattern of
use and traffic congestion on the Internet. This
means that both services will rarely -- if ever --
reach peak performance.
Furthermore, cable modem technology delivers
shared bandwidth within the local neighborhood
while DSL delivers dedicated local bandwidth. With
cable, performance at any given time depends on
how many cable subscribers in the neighborhood are
currently actively using the network as well as load
on the Internet generally. This "double whammy"
suggests that cable modem will perform relatively
slower during peak usage periods.
http://compnetworking.about.com/library/weekly/aa111200b.htmI'll post some personal numbers when I've had a chance to run some tests.