Thanks for the comments Tim/Steve and olderplayer.
Definitely will take some of those things into consideration. I really do like the KoS but I have a very nice FW Khorne DP that doesn't see enough light. This way it will; I still think the Bloodthirster is a honest choice. If you can manage to get that LoL spell off which boosts T by 2/4 he becomes nigh untouchable with even warmachines needing 6's to wound. I think he can still go through blocks of infantry relatively quickly. 7 attacks with rerolls to hit followed by d6 autohits should reasonable take out a decent chunk of models. Just gotta make sure you get something into the flank pretty quick.
I am over on my rares, doh. I'll drop the second squad of flamers and the pyrocasters. I think I'm going to throw in a unit of Khorne hounds to follow the thirster around. What size should I look at? multiple ranks?
I already have the bloodletters so I'm not changing to deamonettes - I think they are both about equal anyways. Plus I have my heralds on bloodletters to up the killing power.