I don't see the higher version of Audyssey? The Denon site shows MultEQ for both. The step-up 2113 appears to have MultEQ XT (more filters).
Seems like the room is large enough that you may want to go 7.1 at some time.
I wouldn't sweat the 15 watts difference, since it'd yield less than 1dB increase in volume.
If it was 75w versus 150w, on the other hand, that'd get more interesting, as it's a 3dB increase. Amazingly, still not a whole lot.
I'd consider the remote, any convenience features you want, room-correction software, and the 7.1.
While the 1913 doesn't step up Audyssey and the watts-increase is negligible, I'd say the $80 is easily justified by the greater number of inputs (you'll always need more than you anticipate) and the additional two channels, and other features like 12v trigger.