The Haswell Xeon E3 series is quad core, single-socket. It uses the same die as desktop Haswell CPUs. The Mac Pro is six core, double-socket, so it must be a "-E". Based on the availability date (later this year), it must be Ivy Bridge-E. Intel will almost certainly call it an E5.
They're advertising quad-channel DDR3-1866. That entirely rules out the desktop-class processors, which have never been used in a Mac Pro anyways. The Xeon E3 and E5 lines use completely different die configurations and motherboard sockets, and the E3s don't have enough PCIe lanes to feed all the peripheral connectivity the new Mac Pro will have.
