Except you don't need to OC as far to get the same performance with Ivy. Basically, the 3570k is a better choice unless you've jammed your motherboard's multiplier at >50, or you can get a 2500k for much cheaper.
IPC on ivy bridge is usually around 10% higher than sandy bridge but sandy bridge can usually OC about 5% higher. This means Ivy bridge still ends up with superior performance both with and without OC. Plus ivy bridge supports several major features that sandy bridge doesn't such as pci-e 3.0 and consumes less power. There is no reason to get a 2500K over a 3570K accept for the slightly lower price in some countries.