I just re-cabled my Fostex T40 v1 with Cat6 cable. I modded the single entry into a dual entry and terminated using a balanced 4-pin XLR. I had about 6 feet of Cat6 cable laying around doing nothing. I had read some folks were using it for headphones. I stripped the sheath off and found 8 wires, I think 26awg. There were 4 twisted pairs. I used 2 twisted pairs for each side. I braided the 4 twisted strands, I'll say it is colorful to say the least. It sounds pretty good for a 5 dollar cable 8^). It is stiff and microphonic. I am not sure if a techflex covering would reduce the microphonics, it will not help with the stiffness. I may have used too tight of a braid as well. I used some white shrink wrap from the cups to the yoke.
Chris, I love the fact that you took the stiff sheath off the CAT5 cable, which must make it more flexible and definitely makes it more colorful and attractive. I think your headphone setup looks smart and cool. Kudos to you for doing something awesome at a modest price.