The bike is a Cannondale System Six, C2, SIDI
SI Integration System, FSA, Gossamer
2 x butted AL2014,OS150 Alloy, 120mm/6"
ISM patented 622x13??
63 cm frame Alcalyte
Wheels - Mavic Ksyzium SL SSC
How much wear is there on the drivetrain, is what you should try to find out. 5 year old Dura Ace is still a 5 year old group set. If the components are worn, they are expensive to replace. Even the cassette lists for close to $300. Nothing on a bike lasts forever, and a hard-ridden bike may have hard-ridden, and/or poorly maintained, components.
Has the bike been crashed? Any visible signs of damage to the frame?
In the abstract, Kyserium wheels are good, but again---how hard have they been ridden?
Also, 63 cm is a HUGE frame. I'm 6' 2" tall and I ride a 60 cm. A 63 cm frame would be for someone 6'5" tall, probably.
BTW, the FSA Gossamer crank is nothing special, and a far cry from Dura Ace. You really need to find out exactly what components are Dura Ace, and what are less than Dura Ace.
To give you some ballpark estimate on worth, a 2013 Super Six with a SRAM Rival group and Fulcrum 7 wheels lists for $2750 and can probably be had for around $2500. Fine frame, decent group, and you get the benefit of a new bike warranty (lifetime on the frame). Buying used, you get **** nothing for a warranty.
Did you catch Mpre53's post? Btw FSA Gossamer is lower end FSA. If they are 2008 Ksyriums they are light years behind the current gen Ksyriums starting 2010. The magic question has been asked: are you a very tall guy? It's a huge bike, the biggest they make. Unless the bike has not been ridden much in the past 5 years, you may also need new chainrings, cassette and/or chain.
$2000 bucks could get you a nice 2013 model with a warranty. Personally I think a brand new Supersix with 105 for a couple hundred bucks more would be a better decision. The upside, if he is a good friend you'll have an accurate history of the bike available.
Btw are you asking us for photos? You'd be posting them for us to evaluate, no?