Okay, so I have been historically recommending a medium-end X79 setup over a high-end Z77 setup, such as an Asrock Extreme6 X79 with a 3820 over a Maximus V Formula and a 3770k. However, I feel like this should be fleshed out a bit.
Now, my reasoning, generally, is future expansion. An X79 board is going offer future CPU expansion, whereas an 1155 board, that has a 3770k, has no real upgrade path, except for some of the 1155 Xeons, which really aren't worth the price. If you start with a 3820, which is a little bit cheaper than the 3770k, you have the 3930k, 3960X, and 3970X to upgrade to, including many more (and much more expensive) Xeons. The CPU power is not the only reason I argue for 2011, though; you have 40 PCIe lanes. If you build a medium-end rig, you're probably only getting a single graphics card. If you plan on getting two lower-end cards instead of a single higher-end card, that is a different argument. On Z77, unless you have a high-end motherboard, like the Maximus V Extreme, Gigabyte UD7, etc., with PLX chips, then after 2-way SLI/CF, you will be using 4x PCIe lanes on two cards, at least. This is going to cause serious bottlenecks in the graphics performance, unless you're running low-end cards. Sure, a PLX chip can synthesize PCIe x16 slots, but the latency isn't worth it when you can get a cheaper motherboard for X79 and have native support for 2-way PCIe CF/SLI, 3-way x8 x8 x16, or 4-way x8 x8 x8 x8. This bandwidth can be a huge help for people who have ridiculous setups, such as quad Titans, which need the bandwidth of X79's PCIe lanes for full performance.
GPU and CPU aside, you may also be running servers, VMs, or doing serious rendering/editing. A Z77 setup could work just fine for all of these, but, under serious loads, especially running VMs, you are going to exceed the 32GB of RAM that Z77 limits you to. X79 offers support for up to 128GB of RAM (if you use 16GB sticks), notably on the MSI Big Bang II X79, but more commonly, 64GB on most ATX or eATX boards. Even the mATX boards support 32GB of memory (some Z77 ones do, as well.) And while, sadly, there are no non-OEM mITX X79 boards, you still have a lot more power in a small space using mATX X79 vs mATX Z77.
If I have left anything out, and/or you have arguments for or against a certain direction, please, by all means, post. I'm not here to impose, and if I got something wrong, please mention it.