Well, there are really two things you need to think about when you buy a bike:
1) What kind of frame does it have?
2) What level components does it have?
For the first question, frame material does have a big effect on how the bike feels, but design also has a big effect. You don't mention what kind of riding you do (or think you might do), and that does have an effect on your bike. If you want to put a rack on it, or commute in the rain, some bikes will let you do that, others won't
The second question is also important. Not only is there a difference between product lines (105 vs ultegra), you will also get different wheels and shifters, which also have an effect on how the bike responds.
I think all the high-end carbon bikes are pretty good. Companies with names to protect need to not build crap. But there are a number of lower-end carbon frames made in asia which haven't really been around long enough to be fully tested. My *guess* is that they are going to be fine, and if you get one of those from a name manufacturer, I wouldn't worry about (though it's good to ask what their frame guarantee is).
You're looking in a price range where there will be a tradeoffs on frame materials, component group, etc. What you should really do is find out what your local shops carry, tell them how much you want to spend, and then take some test rides.
I knew within 5 minutes of riding my Madone that I would buy it, so for me, full carbon is a wonderful material. But I had to spend a fair amount to get both full carbon and full ultegra.
Hope that helps.