A couple of points which are worth mentioning.
Cat6 cable is thicker in diameter than Cat5e and is not as flexible mainly due to the "plastic tube" running down the center of the cable. This can also make it more difficult to terminate.
A lot of the "cheap" Cat5e/6 cable is of the CCA (copper clad aluminum) contruction and unless things have changed this cable does not comply with nor permitted under the ethernet standards.
Some reasons why CCA is not a good choice are
- due to its higher attenuation there is an increase in packet loss especially over longer cable runs and/or higher speeds
- With PoE becomming more popular and squeezing more and more current flow over ethernet cabling the higher resistance of this type of cable means there is a real possiblilty heat can build up quicker than it can disipate