1. Cat 6 cable should squeeze more speed out of your connection
2. Cable length - Keep it as short as possible
3. Your best speed results will be between 2 computers with gigabit connections. Internet usage speeds will be lower in most cases.
4. Make sure jumbo frames are set in network properties for your network adapter. Set to the max value which is 9k.
5. Hard Disk speed can bottleneck your gigabit transfers
Hard Drive Delivers SATA-III 6-Gbit/s Transfer Rate
Will a Gigabit Switch Speed Up My Home Network?