In reply to Matt250:
Big fan of Montane Terras - by far the best feel of any vented trousers I've worn to date. I've managed to put holes into two pairs now - but I guess considering the treatment they've gotten it's to be expected.
I have a pair of Berghaus vented trousers, and found that they're just not as good. Too stretchy, quite a lot heavier, buttons are an absolute faff, and too long in the leg (but unable to be shortened easily due to elastic cuffs).