There can sometimes be confusion over whether to use Cat5e or Cat 6 cable.
A lot of this confusion arises from a belief that Cat6 will give an 'all gigabit' network, which is not in fact the case. Unless every single component in the network is gigabit rated then a true gigabit network will not be achiever, as it will only run at the speed of the slowest device.
Cat5e cable of good quality can run at or near gigabit speeds, but it cannot be 'certified' for this use.
Cat6 is designed especially for gigabit use, and is certified to operate at that speed. So the decision is whether you wish to pay the additional cost for cabling that may provide little or no improvement in the performance of your network.
In most cases it makes more sense to opt for Cat5e as it is more economical and performs well.
Many IT professionals, when asked why they specified Cat6 for a particular job, often responded saying they 'wanted the best they could get'. If you find your IT adviser is specifying Cat6 cable for your network, be sure to understand the reasoning for this, and whether it will deliver any appreciable benefit.