I have a new CAT6 cable that's 50 metres long and only performs at 100 megabit. I've tested it in a variety of gigabit ports and it never allows a gigabit connection. Is it the length that's the problem and will cutting it in half to make two 25 metre cables make it perform at gigabit speeds ? i.e. is the length likely the problem or is it just a duff cable ?