Double KOS

Hey all,

Looking at double KOS for a slannesh only army. If I go both 1 exalted gift / 1 lesser gifts I can only take 2 KOS.

If I replace the exalted on both with greater gift I can squeeze a herald of slannesh with ASF on unit in.

Wondering what's better?

Rest of the army consists on 2 x 25 demonettes and 2 x 6/5 fiends. If I go only double KOS

Or 2 x 25 demonettes 1 x 6 fiends and 1 exalted chariot if I got double KOS and herald

Thanks