On reflection, I doubt that it's possible for a typical family to average more than 2, maybe 2.5 unique attractions per hour over a sustained period in the Magic Kingdom. Around 1.5 to 2.0 sounds about right.
For what it's worth, the highest average attractions per hour I've ever seen anyone achieve in the MK is about 4.2 (that was 42 unique attractions in 9 hours, 59 minutes). These were healthy, fit adults who didn't stop for meals, and walked briskly the entire day.
Hope this helps!
Len