Copied from another website..hope it's helpful:
1. What is the difference between CAT5, CAT5e, CAT6, CAT7...
The Simple Answer:
CAT5 is rated to 100M
CAT5e is rated to 350M
CAT6 and CAT6e is rated to 550M or 1000M depending on your source
CAT7 is supposedly rated to 700M or presumably 1000M
Today there is no approved CAT6 or CAT7. While some folks are selling products they call Level 6 or 7, there aren’t even specs for them, making CAT5e the best available option. CAT6 cable is being made with 23 guage conductor wire as opposed to the slightly smaller 24 guage for CAT5e and also has a separator to handle crosstalk better.
Both CAT5 and CAT5e have 100 ohm impedance and electrical characteristics supporting transmissions up to 100 MHz. The differences between CAT5 and CAT5e show in all aspects of performance: capacitance, frequency, resistance, attenuation, and NEXT. CAT5e components were designed with high-speed gigabit Ethernet in mind. While CAT5 components may function to some degree in a gigabit Ethernet, they perform below standard during high-data transfer scenarios. CAT5e cables work with ATM and gigabit speed products. Simply, if you are using a 100Mbps switch, get CAT5e cable instead of CAT5.
CAT5e is formally called ANSI/TIA/EIA 568A-5 or simply Category 5e (the e stands for ‘enhanced’). CAT5e is completely backward compatible with current CAT5 equipment. The enhanced electrical performance of CAT5e ensures that the cable will support applications that require additional bandwidth, such as gigabit Ethernet or analog video.
