To overclock a "K" you will want a Z97 based motherboard.
Planning for sli or cf will add cost.
Is there really a need for dual cards?
For most, playing on a single monitor(excepting 4k) a good single card will do the job, and there are stronger single cards coming in the future.
If you will plan for dual cards, you will want a full ATX motherboard so there can be some separation between the X16 graphics slots to allow extra cooling for the top card.
Past that, all brands are good and will do the job.
Pick your favorite brand.
Here is an ASUS Z97-E for example:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813132287
All such motherboards will overclock to the same conservative limits.
No need for an expensive enthusiast version which caters to record seeking overclockers.
I have become a bit jaded on the subject of haswell cooling for overclocking.
How high you can OC is firstly determined by your luck in the bin lottery.
I had high expectations from the Devil's canyon parts and their better thermals.
I found out that the thermals really do not matter unless, perhaps, you are a competitive overclocker.
Haswell runs quite cool, that is, until you raise the voltage past 1.25v or so.
Once you go past 1.3v, then you really do need very good cooling to keep stress loads under say 85c.
But, the consensus is that voltages higher than 1.30 are not a good thing for 24/7 usage.
I have been unable to find any official Intel recommendation on what is a safe vcore limit.
If you are an enthusiast, you can go higher.
Even if you can handle the heat, how much do you really need that extra multiplier from say 4.4 to 4.6?
My thought is that it is better to use the exotic cooling funds for a quieter and less expensive air cooler.
I suggest a good tower air cooler like noctua or phanteks with 140mm fans.