I guess my question would be...What kind of riding do you intend to do???

I happen to LOVE the feel of carbon. I have been on a bike for
many a year and I personally think that my carbon bike has made me a better rider. I love the way it climbs, and gathers speed. Plus, it shelters me from some of the harshness of the road surface. I have a Trek 5200, but must add I saved for many years before I made the jump. I was a long time steel junky on a Bianchi and then a Terry before I went to carbon. My husband recently went back to steel...he said he just likes it better...and that's o.k. it does come down to personal preferance. I also recently made the decision to keep my "old school" Terry and convert it to Ultegra so I would still have a "touring" frame in the house.

I have seen and test rode all the Specialized bikes that you mentioned. My son is thinking about the Robaix. I find this to be more of a racing machine than all of the other Specialized out there right now. We have an Allez which I often head off to the store or the bank on, and that is fun ride, however it is aluminum
so that makes the ride a little harsh...much more so than carbon.
I believe the Robaix has mechanisms in the fork and rear triangle to give you the "best ride" To be very honest I did not like the Sirrus. I thought it was kind of "junky", but many of the women who ride them here love them.

The secret is...decide what you want to do with the bike, then ride as many of them as you can until you find THE ONE. Belive me, you will know when you have found THE ONE.

bon chance,
karen