What do you a want from your new bike that your alloy Defy does not offer? Weight? (not so hard to achieve) Stiffness (will depend on the tube diameters and carbon layup)? Better components? (Easy upgrade). Exclusivity (Need lots of cash!)
Whilst the Defy has “sportive” geometry, it’s a very nice blend of race, endurance and comfort. Of course the headtube is a little longer than a classic race bike – but only about a cm. The steering is half a degree slacker than a TCR, but you will not notice. The bike is much less of a sportive compromise than equivalent offerings from Specialized and Cannondale which have very long headtubes. Ask Mr Degenkolb what he thinks of his Defy#.
I’d personally recommend the Carbon Defy Advanced with 105 and save for some shiny lighter bits. That frame was £1500 and Bike of the Year in 2013. Great bikes do not stop being great just because they are running 105 – read Ultegra 6700 with better shifting.
#Or me, we have an alloy Defy and a carbon Advanced SL. They are both great. Also have other alloy and carbon race bikes to compare.