@Isaac
Yes, you are wrong. Sorry to be blunt. The reason the S-III program had SPI armor was because it was cheaper then the MJOLNIR series, which I have no doubt it was. And when you're training 1,500+ SPARTANs, you want it cheap, especially since it's even more of a secret then the S-II program. The SPARTAN-IIIs had the exact same augmentation chems that the S-IIs did, plus a few extra. I have absolutely no doubt that an S-III could drive MJOLNIR armor just as well as an S-II.
@Queen,
Yes, you are right. Lieutenants CAN be Naval. HOWEVER, Lieutenant is SEVERAL grades above Master Chief Petty Officer. John-117 was the highest ranked SPARTAN-IIA of the UNSC, and was the leader of the SPARTAN-IIAs. If the SPARTAN-IIB program is anything like the IIA program, then they'll follow through. Likely, the cause of the FNG being a Lieutenant is because of his standing with ONI. Like Carter-259 said, the ONI didn't want him reading the Lieutenant's file. Question is, why? The SPARTAN-II's were very tight nit, almost always knowing the whereabouts of their brethren. So, my take on this is that the Lieutenant is INDEED an S-III, as even Dr. Halsey had no idea the program existed.
@Boryenko
I wouldn't say that you'd be playing as Kurt. Even though he, too, is a Lieutenant (Commander), I just don't see it. Now, as for time-purposes, it is very possible that it is a S-III. S-III Beta Company was activated in 2539, and by 2545, the S-III Beta company successfully destroyed their target, at the cost of the entire platoon save Tom-B292 and Lucy-B091. If this Lieutenant WERE a S-III, I'd put serious money on it being one of those two.
I'm going to agree with Underdogg13 here. Until we know for sure, the Lieutenant may as well be a 3 year old girl. We just don't know. All we can do is speculate.
I personally want to know about Jorge-052. His armor makes me think he's either a CQB or an EOD specialist. In the official Reach poster, he's holding what LOOKS like a big gun (Possibly an M-247 .50 Caliber Mounted Gun), which would indicate a heavy-weapons discipline. So we've got three separate possibilities on what he is.
And finally, I REALLY want to know about that Hellspartan. Definitely looks to me like he enjoys killing with knives, ruthless brutality, and painful deaths. I can't imagine that visor being particularly easy to see out of, though.