Monster - I've got an XC version and at 1/2" taller with the same leg. I'd bet you £1 you'd want a medium. And I'd echo Innes point on reverbs. My 125mm JUST fits for my normal pedalling height: the seat (#/EDIT:) tube (/)seem looooooong. If you're considering one I'd wait til you have if before ordering a reverb.
- when I got mine last year they were pretty rare but I was lucky enough to borrow one off someone on here I'd never met(cheers Stanfree!). But now there are lots and lots of them around me. Where are you based?
-Canyon are an online business model - and this pisses some folks off. Expect that if there is an issue/ failure : it will all be done by email and hopefully resolved in your favour. But it can be quicker or slower than an lbs purchase in case of problem. Components are covered / fixed by UK suppliers. In the rare (*afaik) case of frame problems it has to be shipped back to Germany.
-Lasly their "UK phone centre" thing is just bobbins. No one ever answers. Although last week I got an email about my complaint on this to say they have employed someone extra (I'd guess that brings the UK staff up to 1 tbh).
Overall - I'd say it's probably a bargain, especially if you're able to handle small fixes yourself. If you want babysitting with questions and issues then maybe look more locally. HTH.