I've done at least 6 centuries on my Trek FX 7500 as well as a 560 miles aids ride (7 days). The FX7500 (similar to the current 7.5) is a bit lighter than the 7.3 but if you train for a century on the 7.3 it will do wonders for your fitness I'm sure!

Perhaps swap out the tires for something a bit narrower/smoother?