I think the question is more theoretical nature. If you start to accelerate at 800 ft with a V/S of 100ft/min to 250 kts you could temporarily find yourself below the OIS even though your average climb gradient is more than 5 % to 4000. I would say that you have a completely free climb rate as long as you stay above the 5 % surface. Imagine you hit 3950 ft at the DER in you Learjet. I would say it's perfectly safe as long as you climb the remaining 50 in the next 12 NM. On the other hand it's not ok to stay at 50 ft for 11 nm and then do a near vertical climb to hit 4000 by 12 NM (both 5 pct average).