depends on the chip; despite being the same model, not all cpus are created equal and OCs differently. so no way of fully knowing till you give it a try.
4.2-4.3 is usually around the spot when you're expected to raise voltage and hence more heat, which is worse in IB's case. though if you're extremely lucky, like one forum user here, you can hit 4.5 without a hitch, on air cooling alone. above that, many would advise you to invest in a custom water loop.