SB out overclocks IB by a large margin..... IB out overclocks HW by a smaller margin. If ya make the argument that IB is better then HW because it overclocks better, well then the same argument applies to SB over IB.
At stock HW > IB > SB so by the time ya get done OC'ing, ya pretty damn close to the same place with all 3.
If ya already have SB or IB, there's no reason to upgrade. If ya on a tight budget and can save a substantial sum of money going w/ IB, I'd do it. But....if the cost is close, ya got the money or don't want to risk obsolescence (socket 1155 is dead), then id get HW.
Lose ya MoBo down the road and with 1155, your MoBo swap becomes a MoBo / CPU swap as 1155 socket MoBo will go the way of the dinosaur in the near future.....try finding an 1156 MoBo on newegg today .... been there done that twice in last 2 weeks ..... one biostar available ..... and both $125 MoBo wound up becoming $350+ MoBo / CPU swaps.