2009 Giant Defy 3.5 to 2013 Giant Defy 1

Hi, I've been looking to buy myself a new bike for a while now but for one reason or another something always comes up to scupper my savings.
I currently ride a 2009 Giant Defy 3.5 which I've gotten along with great but it's had some miles put onto it and it's beginning to get a little tired.
My workplace are about to implement a Cycle to Work Scheme and have agreed to use Cycle Solutions to provide bikes. I've looked at a few bikes at and around the £1000 mark such as the Giant Defy 1, Scott Speedster 20 and the Felt Z85.
I can try out all these bikes locally and I know that the Giant is the best regarded bike for that price bracket, what I'm wondering is if the new Defy is that much different to my current bike if it's worth trying it out knowing I like the current ride or would it be wise to check it out against the other rides in my list.