If an mATX mobo can meet your current and projected future needs, there's no reason not to choose one.
Without knowing whether you want to protect aginst future SLI or CF, and how far you want to OC, and whether you need other expansion slots or legacy support . . . can't really be more specific than that.
Edit: The cheapest Z68 mobo available at Newegg that supports USB 3.0 is an mATX mobo.
It all depends on what features you are looking for. I will assume you do not have a case yet. If the size of the case does not matter, then all you really need to do is determine what features you are looking for. If the mATX mobo has all the features you want, then go for it. The only bad thing about a mATX mobo is the limited expansion slots. However, in many cases the only card installed in a PC is the video card. Since all mobo have built-in audio adding an audio card is not absolutely necessary unless onboard audio sounds bad.
Just be aware that high end do not always mean high performance. The only way to determine if one motherboard offer better performance than other motherboards is to read a review that compares various mobos using the same hardware (CPU, video card, etc...). From what I can remember, the average "high end" mobo only performs 2% or 3% better than an average mainstream mobo. While it they can give you some nice benchmark scores, in the end you will most likely not notice any difference.
I have not done any research on the Asus Maximus 4 gene-z or a Gigabyte Z68 ud3xp (not looking to upgrade yet), therefore, I recommend you look for reviews that compares those mobos to other mobos if you are trying to squeeze the most performance out of your system.