Be careful about the real difference in seat tube angle between the Mach4SL and the new Epic. The Spesh has got a shorter headtube that defines a different measuring point for the effective seat tube angle (stack height is ~4cm less on the Epic). Real world difference between the bikes will be marginal when both run a 100mm fork. It all comes down to personal preference, but I would never trade in a DW Link driven Pivot for a Brain equipped Specialized.