Not to sure now when looking at Cat5e specs it was designed to support Gigabit ethernet transfer speeds of 1000,000 kbps which is a heck of a lot more when your modem HG612 on a 80/20 service only sends and receives 80,000 kbps DS and 20,000 US.
heres a cut & paste
Category 5 vs. 5e
To support Gigabit Ethernet, a higher performance version of cat 5, enhanced cat 5 or cat 5e has been added to the standards. Cat 5e adds new performance requirements to permit higher speed network operation.
The category 5e specification improves upon the category 5 specification by tightening some crosstalk specifications and introducing new crosstalk specifications that were not present in the original category 5 specification. The bandwidth of category 5 and 5e is the same – 100 MHz.
The differences between category 5 and category 5e are in their transmission performance. Category 5e components are most suitable for a high-speed Gigabit Ethernet. While category 5 components may function to some degree in a Gigabit Ethernet, they perform below standard during high-data transfer scenarios.
Surley the CW1308 cable would be able to handle a 40/10 service without any bottlenecking at 17 Mhz