That Focus CX bike was on my shortlist but in the end I stuck with Cannondale ...
I'm sure that it would be almost as nippy as my CAAD5 road bike if it had narrower, slick tyres on it. If you wanted to run just one bike and could afford it, I'd suggest getting a CX bike and an identical second pair of wheels. Have CX tyres on one, and slicks on the other, then it would only take a couple of minutes to switch the bike between road and offroad modes by changing the wheels over.