As the category number gets higher, so does the speed and Mhz of the wire. This is not a coincidence, because each category brings more stringent testing for eliminating crosstalk (XT) and adding isolation between the wires.
This does not mean your experiences have been the same. Physically you can use Cat-5 cable for 1 Gb speeds, and I have personally used cable longer than 100 meters, but because the standard has not been tested for it, you’ll probably have mixed results. Just because you have Cat-6 cable, doesn’t mean you have 1 Gb network speeds either. Every connection in your network needs to support the 1 Gb speed and in some cases, the connection will need to be told in software to use the available speed.
Category 6 was revised with Augmented Category 6 (Cat-6a) which provided testing for 500 Mhz communication (compared to Cat-6’s 250 Mhz). The higher communication frequency eliminated alien crosstalk (AXT) which allows for longer range at 10 Gb/s.