I agree with noobs argument that the house always wins.
If you can kill a mob using a plain vanilla opalo, then you should unless the regen/armour decay adds too much cost.
Although using a marked up sib weapon with a big amp theoretically gives more eco, thus saving you some pecs here and there, the cost of lag misses is not included in this calc, neither is failure to use a finisher or the choice of a mob.
and all that is simply the cost side. the loot side, although mindark/fpc categorically deny this has been really deminished since vu 9.4
I know this because I work with typical loot vs cost to kill a mob.
typical loot:
shoot 100/200 of the same mobs, exclude mini's and globals, write down the tt worth of all the loots and calculate the typical loot of a mob
then kill 50 mobs using a particular gun setup, count the shots/decay and write down the cost to kill a mob
I found sometimes a breer/m2a combo is more expensive then opalo if you don't switch to a finisher, or if you have lag misses. lag misses simply hit you harder on the cost side if your gun is bigger.(because lag misses aren't a constant factor it doesn't even out)
Using this method I now no longer hunt particular mobs, because I have seen the cost to kill vs typical loot balance shift in a negative spiral.
For example, the molisk does not have the same typical loot as it used to have. This is due to certain items no longer dropping from Molisk ,also the cost to kill has gone up due to higher regen, and typical loot didn't go up with the cost to kill, also the price of teeth has plumeted.
Typical loot was 78 pec for molisk young. cost to kill using an amped opalo was 65 pec. Now the typical loot is as low as 45 pec while cost to kill has gone up to 80-100 pec.
This situation is continuing as time progresses.
There are mobs I now avoid like the plague, because I know they won't loot. ( faul, caudatergus, small merp etc)
The only mobs still worth hunting (with a low setup like amped opalo) are snables, exarosaur, drones, argo, atrax and berycled