it will be better with CAT 6..it performs better than CAT5 (this is my opinion)
To be certified for GigE (1000 Mbit) connections you need to use CAT6. However CAT6 is much more expensive. If you aren’t planning on deploying GigE to the users desktops then CAT5 will work just fine. CAT5 will support GigE is just won’t be certified for it. The basic difference between the two is that CAT6 has more shielding.