It doesn't make any difference if you use CAT5, CAT5E or CAT6 as long as all 4 pairs are wired in the cable as per the EIA/TIA specification if you plan on operating the radio's Ethernet interface as 1000Base-T.
The IEEE 1000Base-T specification supports the use of Cat 5, or enhanced Cat 5 cable, for successful gigabit transmission. Cat 5 cable is typically unshielded twisted pair, containing four twisted wire pairs. Fast Ethernet (100Base-T) and 10Base-T use only two of these pairs, leaving two pairs unused. Gigabit Ethernet (1000Base-T) uses all four pairs.