I really don't keep up on this stuff much, but why is this still Haswell based? Why not just do this on Broadwell?
They probably do this because it's probably to easier to manage the larger die size and greater complexity as the process has matured and yields have improved.
For a given CPU that comes off the production line, the max frequency it can run at will vary from chip to chip. As well, if there are dead cores on that chip they can just disable them and sell the chip at a lower price (though, intel may not do this; nvidia has in the past with graphics chips).