If you decide to buy the 2400 sticks you may have two scenarios; the first is that it might not work at all and the second is that if it works it will lower the speed to 2133.
A BIOS update would not make any difference.
At the moment a list of compatible RAM is not available, I would encourage the community here to collaborate in regard to this matter.
So, what you mean to say is, you just don't know.
I guess we will have to wait for more of these to find their way out so individuals can test RAM instead of hoping Intel would actually do that for us.