To chip into the "speed of electricity" argument - why is it applicable!? The greater part of the physical path between us and France is fibre, which means that you look at the speed of light. Furthermore, the greater part of the latency will actually be because of routers in the path, each of which has to look at the packet headers to decide where it should go (to simplify things a bit). If you have a few router hops (which you will have, look at a tracert), you add significant latency.
When looking at the speed of electricity, what are you looking at? The speed of the EM wave, which is quite fast, or the speed of the electrons themselves, which is relatively slow? Both can be determined quite easily, but will not be constant over the connection. The speed of the EM wave will be different on your ADSL line than on a FE/GE line, because they operate on different frequencies.