Cat 6 and cat 5e advantages?

Cat5e is required for the standard for gigabit ethernet; cat5 is only good for up to 100Mbps. Cat6 is better than cat5e; it will probably give you lower signal degradation over longer distances and less interference from external sources, which can improve speed and quality of connections. You could run gigabit ethernet over normal cat5, but the standard makes no promises about how well it will work.

Cat5e and cat6 differ from cat5 in having more twists per inch, which reduces interference at the cost of using more copper.