like Hamster said, 43 is on the small side, 49 is on the big side...

quality wise, a Spec allez is a well put together machine with components that are equally matched.
When fit is not the issue, it's all about the wear of the drivetrain components. Some 10 yr old bikes have seen very few miles, so the stuff is almost new. Some have been riddden hard and put away wet...
Pics can't tell much. Bikes usually look better in pics than they are in real life. My bikes all look great in pics, but when you see some of them, they obviously have had some hard mileage...
If a bike looks worn in pics I expect a basketcase in real life...

bottom line - we can't give the definitive answer, online. If you're not clued enough to make a decision on a used bike, then you need to have someone fill that need, locally. OR, take a chance... and if the bike needs more work than you expected - expect to have it done or do it yourself.
OR
find a LBS whom you can trust to steer you properly in buying a new bike.

every day, your type of query pops up on the 41, the bottom line is always the same...

if you're set on buying a used bike (which can be a great way to go... or not...) then I would say the best possibility for fit will be in sizes 46-48. Then if it looks well maintained in real life, it'll likely be the best chance for no big surprises...

best of luck
let us know how it all comes out