Defy Advanced 2 or 3??

[Ironman]

Hi Guys
I am in the fortunate position of being able to shop for a new bike!

I currently have a Giant Defy 2 2011 which is great but want to go carbon so have been looking at the defy advanced 2 and 3. Now the only real difference (apart from colour!!) is the shimano 105 and the Ultegra set up as far as I know!!.
So my question is -is it really worth the extra 500 quid for the advanced 2 bearing in mind that the current 105 set up is basically the old Ultegra more or less?
Anybody had any experience of these two??

Cheers
IM

p.s Did take a sneaky look at a Willier Gran Turismo, any good in comparison to the two Giants??

[itsnotarace]

Specs look identical apart from the groupset, so not worth £500 difference. The question is whether it will be worth £2000 to change from aluminium to carbon.