better power phases, SLI support, eSATA, etc.
Err, he asked what he would get from buying a more expensive board than Extreme4 from a different brand, not what he would get from buying Extreme4 over a cheaper board. Extreme4 has 8+4 phase power, better than most its competitors at that price range. Extreme4 also supports SLI, and it has an eSATA 6gb/s port.
Shephard: A board from a different brand would be full width ATX which is worth something as it can make cable management holes and RAM slots more accessible, and as pointed out it can also better secure the motherboard on the standoffs.
A more expensive board from Asus or Gigabyte, for instance, could have better BIOS options. Asus has the best fan control settings. Some premium boards closer to $200 have Wi-Fi support, more SATA 6gb/s ports, and more troubleshooting options. So for the most part, Z77 boards beyond the cost of Z77 Extreme4 aren't worth it. But there are similarly priced SLI boards that you should also take a look at:
Asus P8Z77-V LK and
Gigabyte Z77X-D3H.
Are you even sure the Z77 chipset is the right for you? Are you going to be overclocking an unlocked processor? And do you really need SLI/Crossfire support - why not just go with a Z77 Pro3 or Pro4?
I don't know what you mean by power phases.
It refers to the motherboard's power delivery to the CPU, RAM and the iGPU. It's expressed in a+b+c, where a is the number of phases to the CPU, b is to the RAM and c is to the iGPU. The iGPU phases are often left out so it's just expressed in a+b, e.g. 8+4 for Z77 Extreme4.
Phases are all part of the motherboard's voltage regulator circuit. Let's look at CPU phases, for instance. All the phases supply the same voltage to the CPU, but they don't do it at the same time, they do it one at a time. I.e. the voltage goes through the number of phases on the motherboard and then starts over. This means that the more phases you have, the less load there is on each phase, which results in more stable voltages and better longevity per phase.
This is a good thing for overclocking, but it doesn't necessarily mean you should spend a lot of money just to get a few more phases. The power requirements of Ivy Bridge processors are relatively low, so I would say that a mainstream overclocker will be fine with just 4-6 phases on the CPU. 8-phase and above is really only useful for more extreme overclocks.