Meeeeeh.
Don't really think there's need for more opinions. The 3570k is just a 2500k with a smaller die size. Performance is basically the same, but because of the die shrink you get more in it, like the better RAM controller and better build in graphics - hopefully you wont be using them anyway, but still nice to know if your graphics card packs in, you could still play games at decent settings with the integrated graphics.
Also, the Ivybridge will hold their value better now than Sandybridge.
Just seems a no brainer to me to buy Sandy now