The specifications you should look for in a CAT 6 cable for Ethernet and also can be used for HD video distribution are:
- CAT6a- a shielded twisted pair cable.
The outer shielding provides some immunity from extraneous noise
- Look for a wire gauge that is 24AWG or better. The thicker in general will be better
- TIA-568-B. Most are B, but just double check. This spficifies the specific crossings of one of the pairs
- Also for HD video, you want to avoid running the cables thru extraneous wall plates, couplers and terminal jacks.
It is fine for 10/100mbps ethernet data but not recommended for HD video distribution.
- Also avoid running the cables in loops. Make it straight as possible.
Here is some info on CAT cable recommendations