As no one will pony up an answer I'll take a poke. I've ridden all 3. I'd go with the Secteur. I was very impressed with the ride on the Secteur. It's more relaxed than the CAAD or the Allez. The Secteur will be less twitchy and more of an upright ride. It should be more comfortable for a guy you're size. I think you would fit on the Secteur better than the other 2.
I did not like the CAAD at all. It was a harsh stiff beast. It would respond instantly to power or steering inputs. Great if you're racing. But for you're stated purpose I'd say nay. It's a great bike but porbably not for you.
The Allez was smoother than the CAAD. Less sensative to inputs, but quick to respond. It was very plesant to ride for a racing oriented bike. I just think you would feel cramped on one. My opinion only.
So that leaves Secteur. It will take larger tires. It also has stouter wheels stock. You may be able to ride them without spending for wheels. Ask the bike shop you get it from. There input will help. I think it's you're best bet in my opinion.
Now I'll suggest you get out there and ride all 3. Make up you're own mind. We can suggest, but ultimatly it's you're butt ya gotta please. If you can't find you're size. Try one of each in the largest size you can to get a feel for them. Then order the biggest one you can.
Good luck in you're search. And post up pictures of you're new ride when you get it.
Mark Shuman