the next most logical explanation is written on HT's T-700 box: that the 700s are mass troops (likely never given human flesh), not infiltration units like the 800s.
Let me stop you right there, and refer you to the source material, James Cameron's original movie,
The Terminator. Eveything the makers of TS needed to know about 600s is in what Kyle says.
"The Terminator’s an infiltration unit
(not a soldier, not a motorcycle, not a tank, but an infiltrator). Part man, part machine. Underneath it’s a hyper alloy combat chasis. Micro processor controlled. Fully armored. Very tough. But outside it’s living, human tissue. Flesh, skin, hair, blood, grown for the cyborgs. The 600 series had rubber skin
(this is the only mentioned difference, but everything already described must still apply); we spotted them easy
(because their skin didn't look real enough, perhaps it looked more like a 1:1 scale Hot Toys muscle body, not because they were huge and wore rubber masks). But these are new; they look human (not because of more human proportions, but because of the following description). Sweat, bad breath, everything. Very hard to spot. I had to wait til he moved on you before I could zero him.”
So that settles the argument on McG's 600s, but it also suggests that the only difference between 600s and 800s is the skin, so there really was no 700s at all. In both of Cameron's movies, the progression of Terminators is even numbered: 600-800-1000. We're not supposed to have 700s, or even 900s, or Cameron probably would have mentioned it somehow in either script. At least McG realized that before the movie was released and even changed it himself.
For all those that say they did not see any "active" T-700's in the movie may I draw your attention to the opening scene where the chopper lands on an endo and then Conner shoots it in the head, that was a T-700.
Cheers
Mario
It was a 600. Take a look at the skull of your own exibit 'A' more closely.