We used Cat6 in the contract so that it would be more future proof.
I've done some google research that indicates Cat6 is better for streaming applications not yet used widely across the US. (Video over IP to TV set-top boxes, etc)
Found a switch roundup while doing gigabit switch research in which the tester tried both cat5e and cat6.
Though I no longer have the link, the cat6 clearly showed less packet error and faster transmition speeds (by average of 100mbps or more).
The tests showed one switch he was testing with Cat5e at 750mbps, 3% loss. Cat6, 899mbps, 1% loss. I forget his testing methodology, but seemed reasonable, large files, mutiple tests, etc.
I'm just frustrated with the opposing realtor/builder team.