Here's the Excel spreadsheet I was using to simulate 25000 spawns if anyone wants to pick it apart or mess with it. You can change that "Max hours Class R has to kill a mob" value from 8 to whatever. Class C and FFA mobs are assumed to die within an hour, based on P99 raiding history.
[You must be logged in to view images. Log in or Register.] This does not include the extra 3 re-pops per month on average, I just wanted to get a feel for how a delay in killing every third spawn might impact the spawns per month on the non-"forced full re-pop" spawns. The answer was: Not much.
http://www.filedropper.com/spawns