I think the 720 was their top of the line touring bike in the 80s. The 520 is what they have now, but at that time the 520 was the lesser of the two. The 720 is supposed to be a wonderful bike for fully-loaded touring. When DH was looking for an older touring bike, we were hoping he'd find one of those. Alas, at 6'-5", you don't always get the pick of the litter.
The Warrior Princess: 2008 Jamis Xenith Pro / Bontrager Affinity 1 (men's)
2006 Trek Fuel EX 9 / Bontrager Race Luxe
2007 Trek 520 / Serfas Terazzo
Amelia Pond (She travels long distances, has great adventures, and she's a redhead): 2007 Trek Pilot 5.0 / Bontrager Affinity 2 (men's)