SB starts to throttle mid 90's. individual cores can go to mid 90's with the recommend < 80C.
From what I've read SB is easier to OC and Not as sensitive to voltage (SB - Max 1.5, recomended <1.4V).
Upto 5.0 with "Good" Air. My self, Upper 50s -> Low 60's @ 4.6 W/Zalman 9900 Max
IB is only about 10 -> 15% higher performance on a clock per clk basis.
But Most likely could hit Higher Freq with SB easier which would negate that (Just my guess).
Real Good read on OCing IB:http://www.anandtech.com/show/5763/undervolting-and-overclocking-on-ivy-bridge