CPU-Z will not give you the CPU's actual stepping. What CPU-Z does provide is a very generic revision number; it does have a field called "Stepping" that's filled in, but that's not what's being asked for here.
Stepping information is, in essence, a batch number that indicates the type of CPU (dual-core/single-core, production sample/engineering sample/etc., amount of L2 cache, memory controller version, and production date) that you have. Statistical analysis of steppings collected by various intrepid overclockers seem to indicate that certain batches overclock better than others. It doesn't actually indicate that your particular CPU will reach a particular frequency, but it may indicate a certain statistical probability. As always with statistics, the law of averages will apply.
Just remember that, in overclocking, the only guarantee is that there are no guarantees vis-a-vis your performance potential. In other words, YMMV.
Good luck, and hope this helps!