Sandy Bridge CPUs are better than Ivy Bridge CPUs in two areas.
1. Lower TDP when overclocking.
2. Higher overclocking potential.
It is well known that Ivy Bridge CPUs cannot be overclocked as high as Sandy Bridge CPUs due to the high TDP as a result of OC'ing. However, it seems many IB CPUs can still achieve 4.5GHz w/o many issues. Also, the IB CPUs have on average 4% better performance than SB CPUs. Therefore, an IB CPU @ 4.5GHz is about equal to a SB CPU @ 4.7GHz.
Overall, IB CPUs consumes around 15w - 20w less than SB CPUs when stressed. Small, but measurable.
IB CPUs support a PCI-e 3.0 interface while SB CPUs treats a PCI-e 3.0 slot in a motherboard like a PCI-e 2.0 slot. Not a big deal now since no single card can saturate a PCI-e 2.0 slot's bandwidth, but that will likely change in 2 years. No a big now and if you intend on upgrading in 2 years, then it doesn't really matter which CPU you buy now.
While I have not personally looked into the rumor, I have read statements where the Intel HD 4000 in IB CPUs do in fact help improve performance with a discrete graphic card. Not sure how since I haven't done any research on it. It's not a priority for me since I don't plan on upgrading until next year when Haswell comes out.