I've thought about the zylo 5th as well. Like I said, I ran gk and because he wasn't a sith, he gets no extra dodge and gets demolished by all the other squads of maul and his crew. Even with 100k health protection gk only gets to go maybe 1 out of 3 battles. Also you don't really need a non-sith(pretaunt) because if you have dooku(fastest character) he will go first and be only one out of stealth and essentially be your taunter. He will keep regaining protection back. It's very fun!!
Also Zavage makes the team so much better. He is a complete beast and makes this team much much harder to beat.
http://imgur.com/Bam86vF
http://imgur.com/nSPNN0L
Very nice. Good to know the Dooku zeta is that effective. I was planning on going with him next before Kylo. Interesting about GK in this team. I've seen a lot of people go with that. Every time I face him unless he's got yoda and qui gonn to keep him clean, he just spends the whole fight stunned and gives up the taunt enough to take out other toons first. That problem exists with Kylo too, but he tanks effectively enough, and I usually get at least one outrage, which I think will be a game changer with the protection recovery. If not I may consider sith trooper in the mix somewhere. Good to know about Zavage as well.