Z77 is designed for Ivy Bridge. As the chipset you have is Sandy Bridge, this is not a concern unless you intend to update the processor relatively soon.
As for P67 vs Z68 the biggest advantage for the Z68 is the SSD caching. There are other differences, but the mostly depend on weather you will be using discreet graphics cards or do lots of video transcoding.
This webpage should provide more info: http://en.wikipedia.org/wiki/LGA_1155