So a random google image search made me run across this:

http://cghub.com/images/view/346923/

"Oh cool, never seen this piece of Halo 4 concept art before" I thought. I got curious and started looking around this site which lead me to this:

Link here:
http://cghub.com/images/view/177221/

http://cghub.com/images/view/177222/

http://cghub.com/images/view/177223/

It was a really odd looking spartan that I've never seen before! some kind of weird Mk. V mix armor, I couldn't find anything about it on the halo wikis or TCRF (the cutting room floor, a wiki for beta information on games).

The image comes from a site called CGHUB.com, turns out its like the DeviantART of professional artists and modelers. and it also turns out theres a fuckton of 343i, certain affinity, liquid development, and Bungie employees here both former and current. The artist who posted this says its from "early development" of Wars, and since this is a site for professionals to dump old works I see no reason for him to lie. I know that normal users post their fan-stuff too but from what I've been checking out I'm running across real employees, freelance artists, and former interns of these companys.

Hell searching the other halo games is making me turn up HQ concept arts I've been looking for. I would take a minute and see if your favorite game (halo or otherwise) has some neat or never before seen concept art posted their:

http://cghub.com/

Just thought I share, again sorry if this is slowpoke old news. :)