cgrew: But from what I've seen with my own eyeballs the better cables ran faster
There are no speed issues here, it's all going out from the source at the same rate. Any degredation in signal quality is because it's not getting to the display device with the same arrangement of 0's and 1's as when it set out. This could be due to mechanical issues, such as connectors/oxisidsed electrical surfaces, dodgy wires in the cable etc, or it could be due to external interference not being shielded out sufficiently.
The general belief around here is that you start near the bottom and work your way up through the quality and price bands until you find something that works reliably. A monster cable at $250 IS better than a cheap cable at $5, but a cable at $20 may have worked on your particular setup just as well as the $250 one if you'd tried it.
That's about it really. If the info gets to the display device uncorrupted, then there is no difference if you then shield the cable some more etc.