But you can make an educated guess based on previous CPUs. I.e. based on previous experiences, does a Tock usually overclock about the same as the corresponding Tick that use the same manufacturing process?
It varies. Conroe clocked significantly worse than Cedar Mill at 65nm, but it also brought substantial IPC improvements on a scale not seen since.
At 45nm, the initial C0 revision of Nehalem clocked similarly to the C0/C1 Penryn and Penryn CPUs, but perhaps a little poorer than the E0 revisions of those chips. Nehalem's D0 stepping improved clocks to the point that they met or exceeded the capabilities of many E0 Penryns. Keep in mind that Nehalem's die size was 263 mm2, vs 107 mm2 for Wolfdale, the dual core Penryn. The combined area of the two Penryn dies used for quad core Yorkfield CPUs was still smaller than Nehalem. We never saw how well Havendale - the dual core Nehalem - clocked, as it was cancelled at the B-0 stepping.
At 32nm, Sandy Bridge improved clock potential by about 500 MHz over the six core Westmere processor. (ie 4.2GHz to about 4.7 GHz)
There is truly a multitude of factors that affect clock potential, so it really is impossible to say how Haswell will clock at this point.