For me it seems roughly 10 pounds per minute in the 5k. My recent times are 28:45 at 275, 27:21 at 260, 22:52 at 215. Bigger break in-between the last two times obviously. Training has been more or less the same from a time/effort perspective. Heat increased significantly better the last two times, which is a big effect for fatties like me.
I still have a lot of weight to lose obviously and am not exactly as highly trained as the typical letsrunner.
Hopefully will see how well my theory holds up at 175 by the end of the year, am hoping to go sub-20.