Hi there.
Well, it's all depending on your enemie's strength, if they are weak, they will get to the low HP treshold sooner and die sooner still. but does it realy matter with weaker enemies? NO, it's with tougher enemies that you need all the oomph you can get and it is in my opinion, that you may as well have constant higher damage than more damage when they're almost dead, because you have to get them to be almost dead...
PIB00