The motherboard won't likely be the limiting factor in the overclock. Chances are the cpu itself is going to hit a physical overclocking limit far before the motherboard is holding it back, whether it's the most expensive asus motherboard or the z97-a. Especially since you're talking 'ultimate' overclock along the lines of aio coolers and air coolers.
Ultimate overclocking would involve a hand selected 'cherry' cpu (as in a real winner, atypically good overclocker in the silicon lottery) with other preparations like liquid electrical tape for waterproofing the motherboard along with copper pots and ln2. Typical overclocking available to those of us who just cross our fingers for a good cpu, most decent z97 motherboards will do the job, one no better than the other. What usually ends up happening, the cpu starts demanding more than a safe limit of voltage for every day use long before the motherboard power or cpu temps become an issue.
With that said, asus makes decent boards, along with gigabyte, asrock etc. Intel doesn't have the same sort of power issues amd usually suffers from, especially when it comes to the fx 8xxx/9xxx octacores - where it requires a premium motherboard. Pretty much all z97 motherboards are more enthusiast/premium offerings by their nature. It's more about the additional features, m.2 support, sata express support, how many internal sata headers, fan headers, usb ports and so on. Whichever has the ports you need for your setup should handle the overclock just fine. For instance, you could go with an asus maximus vii formula for $309 or an asrock z97 pro4 for $102 or even a gigabyte ga-z97-hd3 for $83 and max the overclock with either an aio or big air cooler. The top end asus for 3x the price won't give you a better oc.
For cpu coolers, just about any of the larger air coolers will handle a max oc. The phanteks tc14pe, dark rock 3, dark rock pro 3, noctua nh-d14/d15, thermalright true spirit 140 power, cryorig r1 ultimate.. lots of them out there. Keep in mind, for some reason pcpartpicker is failing to list many parts or showing them as unavailable when they are in fact available. The phanteks I mentioned and the cryorig models are both unlisted at the moment yet both are in stock and available at newegg (and other places I'm sure).
http://www.newegg.com/Product/Product.aspx?Item=N82E16835709001
http://www.newegg.com/Product/Product.aspx?Item=9SIA4UF1H68938
I'm not as familiar with water coolers, but there's the corsair h100i, h105, h110, kraken x61, thermaltake big water 3.0 etc.
In case you're interested, both asus and gigabyte have been used for world record intel oc's.
gigabyte:
http://www.gigabyte.com/press-center/news-page.aspx?nid=1267
asus: http://www.tomshardware.com/news/haswell-overclocking-hwbot-4770k,27485.html
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