I may be having my wires a little crossed (I'm not an electrical engineer) but I was always under the impression that manipulation of the physical characteristics like that from heat/dampness didn't reduce the "speed" but the "quality" (like line noise/errors/etc) of the line.
Whether old telco lines or newer data lines it's all about electrical signal and bit error rates. More errors = more retransmissions = slower perceived throughput.
Just my thinking.
Reduced quality results in reduced speed. In the best case, you have a technology like DSL that detects the reduced quality, and dynamically adjusts transmission characteristics to adapt. In other cases, you have a technology like Ethernet where misdetection of bits results in the loss of a packet, and ultimately requires retransmission. ... JG -- Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net "We call it the 'one bite at the apple' rule. Give me one chance [and] then I won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN) With 24 million small businesses in the US alone, that's way too many apples.