Does an 8 pair Cat 5 or Cat 6 cable exist?

CAT5 and CAT6 are typically installed as four-pair; it's difficult to find cable containing more than the typical four-pair (8P8C) connections.

Previously, someone wrote that "CAT5 and CAT6 are defined as four pair." The reality is a bit more subtle -- there are separate performance (X amount of crosstalk/loss at a frequency of Y MHz) and cabling specs (Q pins, with pairs ordered as 1-2, 3-6, 4-5, 7-8, cable colors pink, green, blue with polka dots, etc.).

I have found 25 pair CAT5 cable. Cables on Demand, for example, carries this under part number MP-5T90FFUNNA. It terminates in giant RJ-21 connectors on each end. They also make breakout cables to connect to standard RJ-45 ports.

Expect to pay through the nose for this, though. It looks like it runs 85 cents/foot in 100 foot lengths, vs. 5-6 cents/foot for standard CAT5 in 1000 foot spools.