
The problem with Banshees is they are a fragile assault unit in an army with no assault transports.

I like the Shadow Warriors(Sisters of the Watch) a bit more as long as the heads are changed from knight helmets. You could also use Sisters of Averlorn or Shadow Warriors from Fantasy/AoS for some more robed acolytes, but they would need much more work to change weapons. They have good shooting capabilities, tank busting in spades with a lot of melta and multi melta, and recently the new amazing Celestine(Though technically she can go in any army, I think Sisters is the only formations she can join that isn't a CAD or from Gathering Storm I.) To go with your force, you can make a contingent of Inquisition and Acolytes to fill in weaknesses, using a modified Sister of Silence as an inquisitor, and the Acolytes can be headswapped and gun replaced Wych Cult to get some Death Cult-esque acolytes. Their love for all things Melta and Flamer strikes a chord with me, and they can fill in weaknesses w/ allies such as inquisitors and SM.

I have fond memories of DoW: Soulstorm even if it is generally disliked, and they would be more versatile than an all banshee army. Personally, if money is no object, I would go Sisters of Battle.
