Mod Suggestion:
Mob Properties by FatherToast
http://www.minecraftforum.net/forums/mapping-and-modding/minecraft-mods/1282771-1-6-x-forge-father-toasts-mods-special-mobs-mob
It would be awesome if you could make the Mobs a little bit stronger. I think Hexxit was ever a bit too easy. For example: Some Better Dungeons bosses, like the Necromacer are a little bit to bad. You could increase their health or give them Potion effects like Speed or Resistance.
But awesome modpack! I hope their will be a stable version soon :)