Oh... I thought I asked more or less this same thing a few weeks ago and was told that the only reason to add more insulation is to reduce chance of shocks, not loss, so I didn't bother going above 1x for most of my run up to my windmill farm. For that matter, I don't seem to be able to detect any losses at all, anywhere.
I have a LV transformer producing 32v power to run my illuminators and with 8 of them going, it is outputting 2 eu/t, which is what they should consume without any losses. I have quite a bit of copper cable around my base to get the power to the illuminators which should be suffering significant losses running only 32v. I also have a 3x hv cable running from my advanced generators turbine to my MFSU, and while it is only maybe 8 blocks long, it shows the exact same energy in at the input side as out at the MFSU ( though oddly it is not quite as much at the turbine output as it should be ).