I'm about to pull the trigger on my first carbon bike (I have roughly a $3000 budget) Cannondale, Bianchi, Specialized and others particularly advertise a line of bikes that are more comfortable for ultra distance riding. I don't think my LBS will let me take a bike on a really long ride either to really put it to the test. So for those that ride how much more of an advantage is there from let's say a Synapse to a Supersix, given that it is road riding (a little bit of rough shoulder riding at times) and I'm going 80+ mile days?

Also what are your thoughts on the CAAD10? It is aluminum but I've heard great things about it and my budget would definitely make room for getting one with an Ultrega group with some money to spare.