I didnt try the other two you are considering, but I did start thinking I wanted a really light bike. I have wanted a Cervelo R5 with Red ever since I started riding last year. A few months back I bought a 21lbs CX bike and I have been shocked at how fast this was, even with 32mm tires and CX gears. I wouldnt take it on a big climbing route, but for normal rides, and even some hardcore single track it has been fine.
When I went in for the R5, they talked me into trying a few others and once I rode the Dogma it was over. I was afraid it was going to be much heavier but it was about 3/4 lbs difference. (15,4 vs 14.7 apples to apples in size 58) If it was 2lbs heavier, I still would have bought it. The ride and handling are unreal, and the R5 felt somewhat fragile by comparison.
If you can try some of these out. I was shocked at how much I liked the Dogma, and the looks are a big bonus.