To be honest I haven't ridden any of them, but my best advice is to get the once that fits you best. Obviously CF + Dura Ace is the nicest of the bunch, but if you're in pain while riding it, it isn't money well spent. If it fits you right you'll ride more and enjoy it more.

2000Km is roughly 1200 miles, which isn't all that much for a road bike. The drivetrain should have plenty of life left in it. I would want to make sure the bike hasn't been crashed. Look for obvious signs of a crash: scraped paint (rather than scratched paint), scrapes on the brake levers (always a tell-tale sign for me), etc. Good luck and have fun!