Flayer, mikeaus, and scourge for me, and I still run rune-scarred as my only thing above 6. I have won quite a few games off of a sneak-attack into a rune scarred into every clone in my deck copying rune scarred. I think keeping the curve as low as possible is the way to go, but play what you like.
Man, all the hate for burnished hart, I still think it is a solid dude. Leaving 3 mana open makes their removal dead on it, and you can grab that color you are missing or continue to filter your deck. I don't think i would ever get to six-seven mana without it.
i could see with a lower curve that you could drop them, but I would rather not, since landing marchesa is paramount