C5 was replaced by C6 in 2004/5 and was launched in 1997 so is very old by comparison an the C6 is a much better car all round than than the C5. The C6 is now being replaced with the saloons being available since early this year and the Avant's just starting to ship. Late C6's such as the one you mention re well specced mast always with DVD sat nav, phone and leather, s-lines added the usual additions and there was also an s-line special edition (previously known as Le Mans) which added parking sensors, 19" wheels and heated seats, The new A6 (C7) shares its platform with the A7 and has a better ride than the C6 (often overly criticised by the motoring press in my opinion). You'll get the latest sat nav with the option to get google maps integration and keyless start. It also seems to have more space and you get the benefit of the latest engines with lower CO2, but the choice of engines is limited at present (only one petrol option for instance). You will inevitably pay more for a C7 than C6 and will likely find very few if any secondhand especially Avant's. Hope that helps