If it's been good to you, keep the Khorne Herald on Juggernaut. My question, what about taking a second Herald on Juggernaut to replace the Chariot? Skulltaker options? A third Soul Grinder?
I've been sitting here for 20 minutes trying to break this down. I see you're angling for speed, which is good. It ain't an easy decision.
In my experience...
I've never taken Flesh Hounds. I agree that against Grey Knights they'll bring something great to the table, but that 5+ save otherwise means they are less durable than a space marine. They can be tied down by walkers unless Karanak gets stupid lucky.... I think if take any Flesh Hounds, you have to take alot of them. I won't take credit for the idea, but the break-down numbers at the end of this list are interesting to say the least.
http://www.yesthetruthhurts.com/2009/07/competitive-demons/Of course, list is two years old, so grain of salt.
I don't know if I can recommend Bloodthirsters at a competitive level. 250+ is just pricy and can be sunk with a few bad rolls. But they're hella fun! They can handle most anything in the entire game, plus they can blanket themselves in big CC (5+ to hit against, 6+ to wound...) So big upside, big downside.
How conservative do you want to run? The Flesh Hounds will provide consistency, which is a hallmark of successful armies. I have a feeling they're the "correct" choice here. Oh, and I'd take Karanak. Might as well make the squad better while they're alive.
Short of "Red" Scribes, this well has been tapped dry.
