Jeez there is some serious scaremongering going on here.
I know nothing about (Bell?) helicopters, and although to me there is something unnatural about a whole bunch of metal desperately trying to tear itself out of really close formation to achieve flight..
..I take one to work regularly, so Im pretty sure they dont have to fly at 120kts everywhere and I know for sure they can stop, then land - as opposed to the other way about, a safety feature aeroplanes dont have.
I also know that helicopters have altitude/weight performance limitations just like aeroplanes, so no doubt the OP will know these. He has asked about cables and obstacles on charts, so my guess is he is planning this flight pretty carefully.
I would have no hesitation in flying across (over/through) the pyrenees on a clear, low wind day, having meticulously planned the route with margins through the varoius passes and given myself "outs" at strategic points. I have a flight planned through the Alps myself for the summer. In fact its been planned for the last 3 Raduno's to tell the truth, but the weather gods have so far always given me the finger.
It sounds like fun to me, so if you do make the flight, tell us all about it.
Its generally best to make a hole in the sky.......not the ground...