Scott, with my current setup I faced the same challenge! Wife liked the 7.2, but the two Lab5 said 7.4 or Lab3.
So I did an intensive testing with the three different speaker. Suprisingly the lab3 did not work very well as center (at least with the lab5), it always felt ike something is missing.
The 7.2 and the 7.4 did a better job as center speaker, after a full day switching back and force I went with the 7.4 but the difference is much smaller than most would guess....furthermore, a 5.1 setup is mostly used for movies, so once you are pulled into the story of the movie, this little difference is just for the records
So no worries, go with the lab 7.2!
Karsten