So if I wanted to buy a good value for money 650b carbon hardtail, would you guys recommend either of the following:

Vitus Rapide
Boardman

I get 10% off both of those.
The boardman looks to be the better specced one.
Any thoughts?

Might be pushing your budget slightly (no 10% off), and size medium only, but Pauls have the 2014 Scott Scale 720 for £1399 which is an excellent price
http://www.paulscycles.co.uk/m1b8s182p5505/SCOTT-SCALE-720-2014

That’s pretty good, but I’d definitely need a bigger one – I’m 1.92m

As you’re tall what’s the appeal of a 27.5 over a 29?

Better manoeuvrability. I currently ride a 26″ and I borrowed a friend’s 29 and it floats! But I think the halfway house of 27.5 have the advantages of 29s, but retain more nimbleness.

But I’m not a zealot – there are plenty of 29s which I’d love to ride.