Okay, I'll tell you about actual yields. I've mentioned this here before, but I'll share it with you.
About 3 yeard ago, I added a 4x8 tent to my space. I initially set it up with a pair of SE 600s with vented hoods. It was an awesome setup that would yield 2.5 units, give or take an ounce or two. About a year ago, I switched out the 2 600s with 900 watts of Cree and Citizen cobs. I was also able to eliminate the fan that was venting the hoods, meaning I reduced the usage of the tent by 400 watts. I'm now finishing up my 7th run with this setup, and I'm still pulling the same numbers that I was getting before.
Same results - 400 less watts.
Don't get me wrong, if I was building a commercial spot, I'd be leaning twards big DE lights or a combo of DE and CMH.
And like I mentioned in another post, I'm still rocking a 600 in one of my rooms. I'm nostalgic like that.