Mate, if you are going to buy a bike for that much dosh, go to a local bike shop and have it kitted out for your lanky frame especially.
Very true, make sure that frame is right for you by going to a shop. Then order it on-line.
Giant are a well trusted and decent brand, I wouldn't hesitate getting one of their bikes if it fitted well. I'm glad you've gone Road too, hybrids are okay
, but are rubbish on roads compared to a proper road bike (and rubbish off-road compared to a mountain bike).
Seeing as you're spending a lot of money (I go round a slightly creaky - but well looked after - £300 road bike), it is worth brushing up on bike maintenance, lots of places reun afternoon courses, just so you know what every screw does. Obviously lots of stuff on the interweb.
Not sure this is exactly the right one: http://www.bikeradar.com/gear/category/bikes/road/product/defy-2-10-35307
... But do poke around that site, I'm occasionally on the forums (although mostly in summer as I'm a massive wimp).