Can't make up my mind i'm too high

I got this 40"x40"x78" grow tent with a 400watt hps/mh. I also have a 400cfm inline fan with carbon filter that vents outside. The temps are in the very low 70's.
I have this 150watt hps/mh sitting around. Should i bother putting this in as well..... Is it even worth it?
I'm super high right now and can't decide

I probably would, it's more light and already paid for so wh not

How many plants? The con would be extra electricity to pay for if you didnt really need it...

I would work on getting the best use of the light you have first. And get a fan speed controller.. it will allow you to somewhat dial in your temps so your fan is not always on full blast.. just a thought

I have pretty much the same set-up, and also have a 150W laying around, i decided to use CFLs over the 150W simply for space and you can position the cfl's nice and close to encourage some growth with a few good clamps. i havnt been able to source a good 150W grow bulb either..

Burn on.