I just played a game with the second list vs dark eldar and was very pleased with the cultist unit, learning I definitely didn't need two. I had a problem with target priority, the havocs were too clear and painful a target. The ravager was shot down but the 2 raiders stayed in the air all game. I wasn't able to shoot down the pain engine either. Luckily one sorcerer boon of chaos'ed his way into a demon prince. With the invisibility cast on the prince from the other sorcerer, he was able to hold the archon in combat a few turns while the cultists mobbed his incubi retinue to death. WS 1 vs 9 is pretty funny to imagine.
While making this new list I tried to fit huron and a slaanesh lord in but it's too difficult to make all the compulsory troop choices while including an ally. I learned that a sorcerer is not good enough in combat so switched back to a lord. This time giving him a brand and some melta bombs to expand his utility. Outflank rocks as well, however I don't use it often. And while the psychic powers were fun, I just needed more bolters. Adding noise marines back in is my easy fix to this, plus they can march up the field behind the cultists to get into firing range. This should draw some more fire away from the IG detachment so hopefully I can do without the aegis and instead have opted add in some more autocannons in the form of a second havoc squad.
I think the IG detachment is perfect the way it is otherwise. It soaked up a tremendous amount of fire all game. Sadly I passed all my leaderships before the commisar died and didn't have to execute anyone. I now plan to use the gun line to cover the advance of the marines.
Mounted Lord of Slaanesh - Lightning claw, burning brand, melta bombs - 150
19 Cultists - Flamer - 91
10 Marines of Excess - 8 sonic blasters, blastmaster - 264
Havocs - 2 lascannons - 115
Havocs - 3 autocannons - 105
Company Command Squad - Lascannon - 70
Platoon Command Squad - Autocannon - 40
Infantry Squad - Autocannon, flamer, commisar - 100
Infantry Squad - Autocannon, flamer - 65