It's the maximum. Even with the specializations, you have to reach the rank of 10 before you get the armor ability (armor equipment gets awarded at different levels).
I will check my Strategy Guide when I get home and update this answer on how many total assists is needed.
EDIT: Okay, big book of Halo 4 knowledge says
- 25 assists for level 1, worth 250 XP
- 50 assists for level 2, worth 500 XP
- 250 assists for level 3, worth 750 XP
- 500 assists for level 4, worth 1000 XP
- 1000 assists for level 5, worth 2500 XP and grants you the sunspot visor.
Get playing War Games.