Maybe the 100 knot cloud will come with the next stage of global warming
Well if it does it'd mean a surface wind that'd preclude most flying anyway! And if it come while you're up there, no probs as your speed relative to the clouds will never be more or less than your air speed.
Wx can close in behind you. At least it can in England to my certain knowlege, and forecasts are always to be taken as advice, not as gospel, in my book.
No, I've not flown much in Scotland (but have quite a bit in Snowdonia). I don't doubt the locals have been scud running in mountainous Scotland for ever and some have even survived decades of so doing. No doubt experience is an important factor where low cloud, high hills, VFR, and aeroplanes mix.
My point was aimed at the OP, who says he is not experienced. If you know the area well and how the local wx pans out and you have your 'outs' for when it doesn't do what you expected then fine.
Are there many wrecks on those hills? There is in Wales, in the Peak District (much tamer than Scotland), and even on the Wrekin (the only hill for miles around).