Isn't IVY just a shrunk version of Sandy with pretty much the same architecture? If that is the case, I really dont see a big leap in performance. Haswell, on the other hand is a new architecture and the performance leap should therefore be similar to between Santa Rosa and Sandy Bridge.
From what i've read it's not just a shrunk version, it has some improvements that should increase IPC a bit, giving a better performance at the same clock speeds, and the shrink will give it more clock speed AND lower current usage.