dandan – to be honest, a 140mm bike will be better down something like the peaks but maybe look at a beefier front tyre (if not running one already) and just working on your technique a bit.
I've got a Five and it's a truly magical machine but no bike is a silver bullet and the stumpy is still fairly competent. I think it's the case with most 140mm bikes, to really get the most out of them you need to be fit, strong and fast – the Five will look after cautious riders well enough but it really comes alive when you just try and ride the tits off it! (Of course you might be up to this, I don't know, just don't like seeing riders drop the cash and get nothing back for it, when all that was needed was just more time in the saddle)
Btw, I always cringe at the made in the uk argument for the Orange. Mainly cause there's no real proof that they're any better for it. What is important is Orange's evolutionary approach to bike design and the fact that they absolutely only sell something if they like it, ride it and if it survives*.
(*I'm not sure this applies to the G2/G3s)