The difference between P67 and Z68 or Z77 are added features like: iGPU support, Quick Sync, SSD Caching, variants of Virtu with Z68 or Z77. The Z77 additionally offers Intel USB 3.0 native ports and Virtu MVP variant.
Easy to read grid - http://en.wikipedia.org/wiki/LGA_1155
Virtu MVP (review the entire article) - http://www.tomshardware.com/reviews/z77-express-virtu-mvp-benchmark,3174-2.html
For the same money I'd go the Z77 route and if Gigabyte and OC'ing I'd look at the UD5 series.