I have ridden both as I know people who own both these bikes, from my own experiences I would buy the boardman as its a more rewarding ride, it feels like a quality bike. By contrast the Carrera feels like a bike built to a budget and if you really stand on the pedals and bars it feels quite soft, the wheels are nothing short of horrible and accelerate poorly.
The fact is is carbon makes not the slightest bit of difference to me due to the fact not all carbon bikes are created equal and this most certainly is not. The boardman by contrast responds quite well when pushed and has a positive feel to it. I got off the boardman with a smile and impressed with how it compares to bikes of a vastly higher value, I got off the Carrera feeling it was an OK cheap bike. This is where the difference is for me, the Carrera is by no means a terrible bike, its reasonable but feels like your getting what you pay for.
The boardman stands on its own, its not a great bike for the price, its a great bike full stop - I would be happy having one alongside my Venge or Dogma, Look, Dahoon
Having said that different bikes suit different people, you will not truely know till you have a ride, What I or other people think is not important. What you think is the only thing which matters which is why I would never suggest buying a bike without trying it first.