The 550MHz number you saw is just marketing hype. It simply means that they tested it to 550MHz (like a sweep test). Did they say how much positve ACR they had at 550MHz?

You can test it at 1GHz if you want to, but if you don't have positive ACR and headroom then it doesn't mean anything.

Some CAT-5E cables are marketed as 400MHz (Mohawk AdvanceNET). But, that doesn't mean that it has higher bandwidth than CAT-6 which is a 250MHz cable.

The numbers to remember, and the only ones that are important, are:

-- CAT-5/5E = 100MHz
-- CAT-6 = 250MHz
-- CAT-6A = 500MHz

To answer your question... If this is for a commercial app then use either CAT-5E or CAT-6A. If it is resi then CAT-6 may be useful over CAT-5E for supporting 10Gbe in the future up to 55m. Otherwise, you are probably wasting $$

Hans Broesicke, RCDD