You did get it wrong. IB has a comparable OC at a LOWER OC. For example, 4.2 GHz on an IB CPU is equal to 4.5 GHz on a SB CPU.
even still, IB is better. you can OC the SB to say 5ghz and an IB OC of say 4.7ghz the IB would perform better to my understanding
also most people for 24/7 OC stay at 4.5ghz, soo an 4.5Ghz IB OC will perform better then a SB at the same OC