We already have a sticky for this...
Based on every leaked benchy so far:
A: In applications that scale to 8 cores, BD is faster then even the 990x/2600k
B: In applications that do not scale to 8 cores, BD is about 20% slower then the 990x/2600k
Again, leaked benchies, but they've showed the above two rules consistently for a while now. For gaming, I expect BD to be ~15% slower in non-GPU bottlenecked situations.