The structure and dynamics of the financial market are
complex to such a large degree that even experts find the task of making accurate predictions extremely difficult.
A) complex to such a large degree that even experts find the task of making accurate predictions extremely difficult ->"complex to such a large degree" can be said in a better way. Let's move and search for a better one.
B) so complex that even experts find the task of making accurate predictions extremely difficult -> This is better version of A. Let's keep it.
C) complex to such a large degree that even experts find the task of making predictions that are accurate extremely difficult -> I can multiple issues. First, we don't need to say "complex to such a large degree"; we can say "so complex". Second, we are not talking about "predictions that are accurate extremely". Incorrect.
D) complex enough so as to make the task of making accurate predictions extremely difficult even for experts -> Why do we use "so as". Incorrect.
E) complex enough so that even experts find the task of making accurate predictions extremely difficult -> so that is used as a conjunction. But, "so that" is used for defining purpose. For an example, I worked hard in weekends so that I could take leave in next week. In the current option, we don't have purpose post "so that". Incorrect.
So, I think B.