according to the recent leaks/rumors, one can use an sb cpu with ivb pch e.g. z7x or h7x because they're both lga 1155 compatible. but one would lose ivb cpu-specific features such as pcie 3.0 lanes, intel hd gfx 2500 and 4000, quick sync 2, supporting up to 3 displays, default ddr3 1600 ram support etc. this is all speculation, though.
according to rumors, all z68 mobos can support ivb, so can h61, h67 and p67 boards. only b and q series motherboards don't support ivb.
you can always change your motherboard to another one with z68 pch. besides, intel doesn't have good history with backward compatibility. so it is uncertain how ivb cpus' compatibility with sb boards and sb cpus' compatibility with ivb boards would work out in reality.