Harmonic Rhythm
Harmonic rhythm is the rate of chord change.
Hymns that have frequently-changing harmonies (a FAST harmonic rhythm) usually call for a SLOWER tempo. The ear prefers a little more time to adjust to each new harmony.
Hymns that have harmonies that do not change as frequently (a SLOW harmonic rhythm) usually call for a FASTER tempo. The ear is interested in moving through to the next change.